{"id":66484,"date":"2026-10-06T17:21:25","date_gmt":"2026-10-06T14:21:25","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=66484"},"modified":"2026-10-06T17:21:25","modified_gmt":"2026-10-06T14:21:25","slug":"ionic-strength-calculator","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/chemistry\/ionic-strength-calculator\/","title":{"rendered":"Ionic Strength Calculator"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">Find the Ionic Strength of a Solution<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"66484\" data-favorite-title=\"Ionic Strength\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/chemistry\/ionic-strength-calculator\/\" data-favorite-excerpt=\"Calculate the ionic strength of a solution from the molar concentration and charge of each dissolved ion. Enter up to six ion species and get I in mol\/L, plus each ion&#039;s contribution.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-flask\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/chemistry\/ionic-strength-calculator\/\" method=\"POST\" class=\"calculator\" id=\"calculator-66484\" data-post=\"66484\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field\" id=\"input-1\"><label for=\"field-1\">Number of Ions<\/label><div class=\"grid grid-cols-1\"><select id=\"field-1\" name=\"number_of_ions\"><option value=\"1\">1 ion<\/option><option value=\"2\" selected>2 ions<\/option><option value=\"3\">3 ions<\/option><option value=\"4\">4 ions<\/option><option value=\"5\">5 ions<\/option><option value=\"6\">6 ions<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-2\">Concentration of Ion 1<\/label><div class=\"term\">c\u2081<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"text\" name=\"concentration_of_ion_1\" id=\"field-2\" aria-describedby=\"calc-info-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 0.1\" min=\"0\" value=\"0.1\"\/><div class=\"grid grid-cols-1\"><select id=\"field-3\" name=\"unit\" aria-label=\"Unit\"><option value=\"mol_l\" selected>mol\/L<\/option><option value=\"mmol_l\">mmol\/L<\/option><option value=\"umol_l\">\u00b5mol\/L<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-2\">Molar concentration of the first ion (e.g. Na\u207a)<\/small><\/div><div class=\"field has-term\" id=\"input-3\"><label for=\"field-4\">Charge of Ion 1<\/label><div class=\"term\">z\u2081<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"charge_of_ion_1\" id=\"field-4\" aria-describedby=\"calc-info-4\" placeholder=\"e.g. 1\" min=\"-6\" max=\"6\" step=\"1\" value=\"1\"\/><small id=\"calc-info-4\">Charge number with sign (e.g. +1 for Na\u207a, \u22121 for Cl\u207b)<\/small><\/div><div class=\"field has-term\" id=\"input-4\"><label for=\"field-5\">Concentration of Ion 2<\/label><div class=\"term\">c\u2082<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"text\" name=\"concentration_of_ion_2\" id=\"field-5\" aria-describedby=\"calc-info-5\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 0.1\" min=\"0\" value=\"0.1\"\/><div class=\"grid grid-cols-1\"><select id=\"field-6\" name=\"unit\" aria-label=\"Unit\"><option value=\"mol_l\" selected>mol\/L<\/option><option value=\"mmol_l\">mmol\/L<\/option><option value=\"umol_l\">\u00b5mol\/L<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-5\">Molar concentration of the second ion (e.g. Cl\u207b)<\/small><\/div><div class=\"field has-term\" id=\"input-5\"><label for=\"field-7\">Charge of Ion 2<\/label><div class=\"term\">z\u2082<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"charge_of_ion_2\" id=\"field-7\" aria-describedby=\"calc-info-7\" placeholder=\"e.g. -1\" min=\"-6\" max=\"6\" step=\"1\" value=\"-1\"\/><small id=\"calc-info-7\">Charge number with sign (e.g. \u22121 for Cl\u207b, +2 for Ca\u00b2\u207a)<\/small><\/div><div class=\"field has-term\" id=\"input-6\" hidden><label for=\"field-8\">Concentration of Ion 3<\/label><div class=\"term\">c\u2083<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"text\" name=\"concentration_of_ion_3\" id=\"field-8\" aria-describedby=\"calc-info-8\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 0.05\" min=\"0\" value=\"0.05\"\/><div class=\"grid grid-cols-1\"><select id=\"field-9\" name=\"unit\" aria-label=\"Unit\"><option value=\"mol_l\" selected>mol\/L<\/option><option value=\"mmol_l\">mmol\/L<\/option><option value=\"umol_l\">\u00b5mol\/L<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-8\">Molar concentration of the third ion<\/small><\/div><div class=\"field has-term\" id=\"input-7\" hidden><label for=\"field-10\">Charge of Ion 3<\/label><div class=\"term\">z\u2083<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"charge_of_ion_3\" id=\"field-10\" aria-describedby=\"calc-info-10\" placeholder=\"e.g. -2\" min=\"-6\" max=\"6\" step=\"1\" value=\"-2\"\/><small id=\"calc-info-10\">Charge number with sign<\/small><\/div><div class=\"field has-term\" id=\"input-8\" hidden><label for=\"field-11\">Concentration of Ion 4<\/label><div class=\"term\">c\u2084<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"text\" name=\"concentration_of_ion_4\" id=\"field-11\" aria-describedby=\"calc-info-11\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 0.05\" min=\"0\" value=\"0.05\"\/><div class=\"grid grid-cols-1\"><select id=\"field-12\" name=\"unit\" aria-label=\"Unit\"><option value=\"mol_l\" selected>mol\/L<\/option><option value=\"mmol_l\">mmol\/L<\/option><option value=\"umol_l\">\u00b5mol\/L<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-11\">Molar concentration of the fourth ion<\/small><\/div><div class=\"field has-term\" id=\"input-9\" hidden><label for=\"field-13\">Charge of Ion 4<\/label><div class=\"term\">z\u2084<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"charge_of_ion_4\" id=\"field-13\" aria-describedby=\"calc-info-13\" placeholder=\"e.g. 2\" min=\"-6\" max=\"6\" step=\"1\" value=\"2\"\/><small id=\"calc-info-13\">Charge number with sign<\/small><\/div><div class=\"field has-term\" id=\"input-10\" hidden><label for=\"field-14\">Concentration of Ion 5<\/label><div class=\"term\">c\u2085<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"text\" name=\"concentration_of_ion_5\" id=\"field-14\" aria-describedby=\"calc-info-14\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 0.02\" min=\"0\" value=\"0.02\"\/><div class=\"grid grid-cols-1\"><select id=\"field-15\" name=\"unit\" aria-label=\"Unit\"><option value=\"mol_l\" selected>mol\/L<\/option><option value=\"mmol_l\">mmol\/L<\/option><option value=\"umol_l\">\u00b5mol\/L<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-14\">Molar concentration of the fifth ion<\/small><\/div><div class=\"field has-term\" id=\"input-11\" hidden><label for=\"field-16\">Charge of Ion 5<\/label><div class=\"term\">z\u2085<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"charge_of_ion_5\" id=\"field-16\" aria-describedby=\"calc-info-16\" placeholder=\"e.g. 3\" min=\"-6\" max=\"6\" step=\"1\" value=\"3\"\/><small id=\"calc-info-16\">Charge number with sign<\/small><\/div><div class=\"field has-term\" id=\"input-12\" hidden><label for=\"field-17\">Concentration of Ion 6<\/label><div class=\"term\">c\u2086<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"text\" name=\"concentration_of_ion_6\" id=\"field-17\" aria-describedby=\"calc-info-17\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 0.02\" min=\"0\" value=\"0.02\"\/><div class=\"grid grid-cols-1\"><select id=\"field-18\" name=\"unit\" aria-label=\"Unit\"><option value=\"mol_l\" selected>mol\/L<\/option><option value=\"mmol_l\">mmol\/L<\/option><option value=\"umol_l\">\u00b5mol\/L<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-17\">Molar concentration of the sixth ion<\/small><\/div><div class=\"field has-term\" id=\"input-13\" hidden><label for=\"field-19\">Charge of Ion 6<\/label><div class=\"term\">z\u2086<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"charge_of_ion_6\" id=\"field-19\" aria-describedby=\"calc-info-19\" placeholder=\"e.g. -1\" min=\"-6\" max=\"6\" step=\"1\" value=\"-1\"\/><small id=\"calc-info-19\">Charge number with sign<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"66484\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Ionic Strength Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Ionic Strength<\/span><span class=\"result-term\">I<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"mol\/L\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-2\"><span class=\"field-title\"><span>Ionic Strength<\/span><span class=\"result-term\">I<\/span><\/span><span class=\"field-value\" id=\"result-2\" data-unit=\"mmol\/L\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result is-column\" id=\"output-3\"><span class=\"field-title\"><span>Ion Contributions<\/span><\/span><span class=\"field-value\" id=\"result-3\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"66484\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>Ionic Strength Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[ I = \\frac{1}{2} \\sum_{i=1}^{n} c_i z_i^{2} \\]<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(I\\) \u2014 ionic strength (mol\/L)<\/li>\n<li>\\(c_i\\) \u2014 molar concentration of ion \\(i\\) (mol\/L)<\/li>\n<li>\\(z_i\\) \u2014 charge number of ion \\(i\\), with sign (e.g. \\(+1\\) for Na\u207a, \\(-2\\) for SO\u2084\u00b2\u207b)<\/li>\n<li>\\(n\\) \u2014 number of ion species in the solution<\/li>\n<\/ul>\n<p>The formula says that ionic strength is half the sum of each ion's concentration multiplied by the square of its charge. Squaring the charge means highly charged ions contribute far more than their concentration alone suggests.<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>Ionic Strength \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> a 0.1 mol\/L sodium chloride solution, where \\([\\text{Na}^+] = 0.1\\) mol\/L with \\(z = +1\\) and \\([\\text{Cl}^-] = 0.1\\) mol\/L with \\(z = -1\\).<\/p>\n<p>\\[ I = \\tfrac{1}{2}\\left( 0.1 \\times 1^{2} + 0.1 \\times (-1)^{2} \\right) \\]<\/p>\n<p>\\[ I = \\tfrac{1}{2}(0.1 + 0.1) = 0.1 \\text{ mol\/L} \\]<\/p>\n<p><strong>Result:<\/strong> the ionic strength is 0.1 mol\/L (100 mmol\/L), identical to the salt concentration because both ions are singly charged.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the Ionic Strength Calculator<\/h2>\n<ol>\n<li>Set <strong>Number of Ions<\/strong> to how many distinct ion species are dissolved in your solution (1 to 6).<\/li>\n<li>For each ion, enter its molar concentration in <strong>Concentration of Ion 1<\/strong>, <strong>Concentration of Ion 2<\/strong>, etc., and choose the unit (mol\/L, mmol\/L or \u00b5mol\/L).<\/li>\n<li>Enter the charge number with its sign in the corresponding <strong>Charge of Ion<\/strong> field: \\(+1\\) for Na\u207a, \\(-1\\) for Cl\u207b, \\(+2\\) for Ca\u00b2\u207a, \\(-2\\) for SO\u2084\u00b2\u207b, and so on.<\/li>\n<li>Read the <strong>Ionic Strength<\/strong> result in mol\/L and mmol\/L, and check the <strong>Ion Contributions<\/strong> table to see how much each ion adds to the total.<\/li>\n<\/ol>\n<h2>What Is Ionic Strength?<\/h2>\n<p>Ionic strength is a measure of the total concentration of ions in a solution, weighted by the square of each ion's charge. It was introduced by G. N. Lewis and M. Randall in 1921 and has become a central quantity in electrochemistry and solution chemistry. Unlike simple molarity, which counts particles regardless of charge, ionic strength captures the fact that a doubly charged ion disturbs the solution's electrical environment roughly four times as much as a singly charged one at the same concentration.<\/p>\n<p>For a 1:1 electrolyte such as NaCl, where both ions carry a single charge, the ionic strength simply equals the salt's molar concentration. For asymmetric salts the numbers differ: in 0.1 mol\/L CaCl\u2082, ionic strength is \\(\\tfrac{1}{2}(0.1 \\times 2^2 + 0.2 \\times 1^2) = 0.3\\) mol\/L, three times the molarity. This is why ionic strength, not concentration, is the quantity that governs how ions behave in solution.<\/p>\n<p>Ionic strength matters because it controls the activity coefficients of ions \u2014 the effective concentrations that appear in equilibrium expressions. It influences the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/nernst-equation-calculator\/\">Nernst equation<\/a> for electrode potentials, buffer capacity and measured <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/ph-calculator\/\">pH<\/a>, solubility of sparingly soluble salts, protein stability, and the kinetics of ionic reactions. The Debye\u2013H\u00fcckel theory, valid for dilute solutions (typically \\(I &lt; 0.1\\) mol\/L), explicitly relates activity coefficients to the square root of ionic strength.<\/p>\n<h2>Interpreting the Result<\/h2>\n<p>The Ion Contributions table shows each species' term \\(c_i z_i^2\\) and its share of the total. Even a minor concentration of a multivalent ion such as Al\u00b3\u207a or PO\u2084\u00b3\u207b can dominate the ionic strength of a mixture. When you compare solutions, always compare \\(I\\) values rather than raw salt concentrations \u2014 a 0.05 mol\/L MgSO\u2084 solution (\\(I = 0.2\\)) is electrochemically \"stronger\" than a 0.1 mol\/L KCl solution (\\(I = 0.1\\)).<\/p>\n<h2>Assumptions and Practical Tips<\/h2>\n<ul>\n<li><strong>Complete dissociation is assumed.<\/strong> The calculator treats every ion you enter as a free, independent species. For weak electrolytes (weak acids, bases) or ion pairs, enter the actual free-ion concentrations, not the analytical concentration of the parent compound.<\/li>\n<li><strong>Count every ion separately.<\/strong> For 0.1 mol\/L CaCl\u2082, enter Ca\u00b2\u207a at 0.1 mol\/L (\\(z = +2\\)) and Cl\u207b at 0.2 mol\/L (\\(z = -1\\)), since each formula unit releases two chloride ions.<\/li>\n<li><strong>Charge sign does not affect the result.<\/strong> Because \\(z\\) is squared, entering \\(-1\\) or \\(+1\\) gives the same contribution \u2014 but enter the correct sign anyway so the contributions table is easy to audit.<\/li>\n<li><strong>Water itself is neglected.<\/strong> The tiny contribution of H\u207a and OH\u207b from autoionization (10\u207b\u2077 mol\/L each) is irrelevant except in extremely pure water.<\/li>\n<li><strong>Units must be molar.<\/strong> The calculator converts mmol\/L and \u00b5mol\/L automatically, but if your data is in mg\/L or ppm, first convert it to mol\/L using the molar mass \u2014 our <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/molarity-calculator\/\">molarity calculator<\/a> can help.<\/li>\n<\/ul>\n<h2>Ionic Strength of Common Salt Solutions<\/h2>\n<p>For a fully dissociated salt \\(\\text{M}_{a}\\text{X}_{b}\\) at molar concentration \\(c\\), the ionic strength is \\(I = \\tfrac{1}{2}(a z_M^2 + b z_X^2)\\,c\\):<\/p>\n<table>\n<thead>\n<tr>\n<th>Solution (1 mol\/L)<\/th>\n<th>Ions present<\/th>\n<th>Ionic strength I (mol\/L)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>NaCl 1:1<\/td>\n<td>Na\u207a, Cl\u207b<\/td>\n<td>1.0<\/td>\n<\/tr>\n<tr>\n<td>KBr 1:1<\/td>\n<td>K\u207a, Br\u207b<\/td>\n<td>1.0<\/td>\n<\/tr>\n<tr>\n<td>CaCl\u2082 1:2<\/td>\n<td>Ca\u00b2\u207a, 2 Cl\u207b<\/td>\n<td>3.0<\/td>\n<\/tr>\n<tr>\n<td>Na\u2082SO\u2084 2:1<\/td>\n<td>2 Na\u207a, SO\u2084\u00b2\u207b<\/td>\n<td>3.0<\/td>\n<\/tr>\n<tr>\n<td>MgSO\u2084 2:2<\/td>\n<td>Mg\u00b2\u207a, SO\u2084\u00b2\u207b<\/td>\n<td>4.0<\/td>\n<\/tr>\n<tr>\n<td>AlCl\u2083 1:3<\/td>\n<td>Al\u00b3\u207a, 3 Cl\u207b<\/td>\n<td>6.0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>If your work involves colligative properties or transport across membranes, you may also find our <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/osmotic-pressure-calculator\/\">osmotic pressure calculator<\/a> useful, since osmotic pressure likewise depends on the total number of dissolved particles.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the ionic strength of a solution from the molar concentration and charge of each dissolved ion. Enter up to six ion species and get I in mol\/L, plus each ion's contribution.<\/p>\n","protected":false},"author":3168,"featured_media":0,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[54],"tags":[58],"class_list":["post-66484","post","type-post","status-publish","format-standard","hentry","category-chemistry","tag-buffers"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66484","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/3168"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=66484"}],"version-history":[{"count":1,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66484\/revisions"}],"predecessor-version":[{"id":66485,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66484\/revisions\/66485"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=66484"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=66484"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=66484"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}