{"id":66506,"date":"2026-10-06T17:37:43","date_gmt":"2026-10-06T14:37:43","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=66506"},"modified":"2026-10-06T17:37:43","modified_gmt":"2026-10-06T14:37:43","slug":"mass-spectrometry-m-z-calculator","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/chemistry\/mass-spectrometry-m-z-calculator\/","title":{"rendered":"Mass Spectrometry m\/z 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 m\/z of an Ion<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"66506\" data-favorite-title=\"Mass Spectrometry m\/z\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/chemistry\/mass-spectrometry-m-z-calculator\/\" data-favorite-excerpt=\"Calculate the mass-to-charge ratio (m\/z) of an ion from its neutral mass, charge number and adduct mass. Handles protonated, sodiated, ammoniated and multiply charged ions.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-chemistry\">\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\/mass-spectrometry-m-z-calculator\/\" method=\"POST\" class=\"calculator\" id=\"calculator-66506\" data-post=\"66506\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field has-term\" id=\"input-1\"><label for=\"field-1\">Ion (Analyte) Mass<\/label><div class=\"term\">M<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"ion_analyte_mass\" id=\"field-1\" aria-describedby=\"calc-unit-1 calc-info-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 573.35\" min=\"0\" value=\"573.35\"\/><div class=\"unit\" id=\"calc-unit-1\">Da<\/div><small id=\"calc-info-1\">Neutral mass of the molecule or ion in daltons (numerically the same as g\/mol)<\/small><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-2\">Charge Number<\/label><div class=\"term\">z<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"charge_number\" id=\"field-2\" aria-describedby=\"calc-info-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 1, 2\" min=\"1\" value=\"1\"\/><small id=\"calc-info-2\">Absolute number of charges on the ion, e.g. 2 for a doubly protonated peptide [M+2H]\u00b2\u207a<\/small><\/div><div class=\"field has-term\" id=\"input-3\"><label for=\"field-3\">Adduct Mass (optional)<\/label><div class=\"term\">\u0394<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"adduct_mass_optional\" id=\"field-3\" aria-describedby=\"calc-unit-3 calc-info-3\" placeholder=\"e.g. 1.007276 for H\u207a, 0 for none\" step=\"any\" value=\"1.007276\"\/><div class=\"unit\" id=\"calc-unit-3\">Da<\/div><small id=\"calc-info-3\">Mass added by the adduct: H\u207a +1.007276, Na\u207a +22.989218, K\u207a +38.963158, NH\u2084\u207a +18.033823; use a negative value for deprotonation [M\u2212H]\u207b (\u22121.007276)<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"66506\">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> Mass Spectrum Prediction<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Mass-to-Charge Ratio<\/span><span class=\"result-term\">m\/z<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"Da\/e (m\/z)\"><\/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>Total Ion Mass<\/span><\/span><span class=\"field-value\" id=\"result-2\" data-unit=\"Da\"><\/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>Calculation Details<\/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=\"66506\" 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 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<\/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>Mass Spectrometry m\/z 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\\[ m\/z = \\frac{M + \\Delta}{z} \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(M\\) \u2014 neutral mass of the analyte in daltons (numerically the same as g\/mol)<\/li>\n<li>\\(\\Delta\\) \u2014 mass added by the adduct, in daltons (e.g. \\(+1.007276\\) Da for H\u207a, \\(-1.007276\\) Da for [M\u2212H]\u207b)<\/li>\n<li>\\(z\\) \u2014 charge number, the absolute number of charges on the ion (1, 2, 3\u2026)<\/li>\n<li>\\(m\/z\\) \u2014 mass-to-charge ratio, reported in Da\/e (often just called m\/z or Th)<\/li>\n<\/ul>\n<p>The formula gives the position where the ion appears in a mass spectrum: the total mass of the ion (analyte plus any adducts) divided by the number of charges it carries.<\/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>Mass Spectrometry m\/z \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> a peptide with a neutral monoisotopic mass of 573.35 Da is observed as a singly protonated ion, [M+H]\u207a.<\/p>\n<p>\\[ m\/z = \\frac{M + \\Delta}{z} = \\frac{573.35 + 1.007276}{1} = \\frac{574.357276}{1} = 574.3573 \\text{ Da\/e} \\]<\/p>\n<p><strong>Result:<\/strong> the ion appears at m\/z 574.3573, and the total ion mass is 574.3573 Da. Since z = 1, the isotope peaks are spaced about 1 Da apart.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the Calculator<\/h2>\n<ol>\n<li>Enter the <strong>Ion (Analyte) Mass<\/strong> \u2014 the neutral monoisotopic mass of your molecule in daltons (the default is 573.35 Da).<\/li>\n<li>Set the <strong>Charge Number<\/strong> to the absolute number of charges, e.g. 2 for a doubly protonated ion [M+2H]\u00b2\u207a. It must be a whole number of 1 or more.<\/li>\n<li>Enter the <strong>Adduct Mass (optional)<\/strong>: 1.007276 for H\u207a, 22.989218 for Na\u207a, 38.963158 for K\u207a, 18.033823 for NH\u2084\u207a, or 0 if there is no adduct. Use a negative value (\u22121.007276) for deprotonated ions [M\u2212H]\u207b.<\/li>\n<li>Read the <strong>Mass-to-Charge Ratio<\/strong> and <strong>Total Ion Mass<\/strong> in the results, together with the calculation details and isotope spacing.<\/li>\n<\/ol>\n<h2>What Is m\/z and Why It Matters<\/h2>\n<p>In mass spectrometry, an instrument does not measure mass directly \u2014 it separates ions by their mass-to-charge ratio, \\(m\/z\\). That is why two ions with quite different masses can appear at the same position on a spectrum if their charges differ. Understanding \\(m\/z\\) is essential for interpreting spectra, identifying unknowns, and planning experiments, because the peak position is the primary piece of information a mass spectrometer provides.<\/p>\n<p>The charge number \\(z\\) has a dramatic effect. A 10,000 Da protein carrying a single proton appears at m\/z \u2248 10,001, which is beyond the range of many mass analyzers. The same protein with 20 protons, [M+20H]\u00b2\u2070\u207a, appears near m\/z 501 \u2014 comfortably within range. This is why electrospray ionization, which readily produces multiply charged ions, made large biomolecules accessible to instruments with modest mass ranges.<\/p>\n<p>Charge also changes the appearance of isotope patterns. Every ion gives a cluster of peaks from naturally occurring isotopes (mainly \u00b9\u00b3C). These peaks are spaced by \\(1\/z\\) Da: 1 Da apart for singly charged ions, 0.5 Da for doubly charged ions, 0.33 Da for triply charged ions, and so on. Reading the isotope spacing is a standard way to determine the charge state of an unknown peak \u2014 the calculator reports this spacing automatically whenever \\(z &gt; 1\\).<\/p>\n<p>The adduct mass accounts for whatever is attached to the analyte during ionization. In positive mode this is most often a proton, but sodium, potassium and ammonium adducts are common in LC-MS. In negative mode, deprotonation [M\u2212H]\u207b is typical, so you enter a negative adduct mass. Because \\(m\/z\\) depends on the exact adduct, specifying the right one matters for matching measured spectra to predicted values.<\/p>\n<h2>Assumptions, Limitations and Practical Tips<\/h2>\n<ul>\n<li><strong>Use monoisotopic masses<\/strong> for accurate results. Average (chemical) masses will shift the predicted m\/z by a fraction of a dalton for small molecules and by more for large ones.<\/li>\n<li><strong>Use the proton mass, not the hydrogen atom mass.<\/strong> H\u207a is 1.007276 Da; a neutral hydrogen atom is 1.007825 Da. The 0.00055 Da difference matters at high resolution.<\/li>\n<li><strong>Adduct masses should include all attached species.<\/strong> For [M+2H]\u00b2\u207a, enter the analyte mass once, charge 2, and adduct mass 1.007276 (a single H\u207a) \u2014 the calculator multiplies nothing; if you prefer, enter 2.014552 for two protons. For [M+H+Na]\u00b2\u207a you would enter 23.996494 (1.007276 + 22.989218) with z = 2.<\/li>\n<li><strong>The calculator assumes a point charge.<\/strong> In reality, electrons have negligible mass (about 0.00055 Da each), so losing or gaining electrons changes the mass far less than typical measurement accuracy \u2014 it is safely ignored.<\/li>\n<li><strong>Negative-ion mode:<\/strong> enter the adduct as a negative number. The charge number stays positive because \\(z\\) is the absolute number of charges; polarity affects the sign of the spectrum, not the \\(m\/z\\) value.<\/li>\n<li><strong>Common reference masses:<\/strong> H\u207a +1.007276, Na\u207a +22.989218, K\u207a +38.963158, NH\u2084\u207a +18.033823, Cl\u207b \u221234.969402 (for [M+Cl]\u207b adducts, added as a positive adduct with z = 1).<\/li>\n<\/ul>\n<p>If you are working out ion structures and charge distributions, the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/formal-charge-calculator\/\">Formal Charge calculator<\/a> helps you determine which atom carries the charge, and the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/empirical-formula-calculator\/\">Empirical Formula calculator<\/a> is useful for confirming the composition of the neutral analyte. For solutions used in sample preparation, see the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/molarity-calculator\/\">Molarity calculator<\/a> and the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/ionic-strength-calculator\/\">Ionic Strength calculator<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the mass-to-charge ratio (m\/z) of an ion from its neutral mass, charge number and adduct mass. Handles protonated, sodiated, ammoniated and multiply charged ions.<\/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":[56],"class_list":["post-66506","post","type-post","status-publish","format-standard","hentry","category-chemistry","tag-stoichiometry"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66506","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=66506"}],"version-history":[{"count":1,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66506\/revisions"}],"predecessor-version":[{"id":66507,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66506\/revisions\/66507"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=66506"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=66506"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=66506"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}