{"id":59532,"date":"2016-03-25T16:04:10","date_gmt":"2016-03-25T14:04:10","guid":{"rendered":"http:\/\/wpcalc.com\/?p=59532"},"modified":"2026-09-28T14:18:02","modified_gmt":"2026-09-28T11:18:02","slug":"atomic-mass","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/chemistry\/atomic-mass\/","title":{"rendered":"Atomic Mass 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\">Calculator of Atomic Mass (Amu) of an Element<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"59532\" data-favorite-title=\"Atomic Mass\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/chemistry\/atomic-mass\/\" data-favorite-excerpt=\"Estimate an isotope\u2019s atomic mass from its numbers of protons and neutrons. Enter the two counts to get an approximate result in atomic mass units (amu).\" 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\/atomic-mass\/\" method=\"POST\" class=\"calculator\" id=\"calculator-59532\" data-post=\"59532\"><fieldset class=\"fieldset-input\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field\" id=\"input-1\"><label for=\"field-1\">Number of Protons<\/label><input type=\"text\" name=\"number_of_protons\" id=\"field-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0\" value=\"1\"\/><\/div><div class=\"field\" id=\"input-2\"><label for=\"field-2\">Number of Neutrons<\/label><input type=\"text\" name=\"number_of_neutrons\" id=\"field-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0\" value=\"0\"\/><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"59532\">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> Your Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Atomic Mass (Amu)<\/span><\/span><span class=\"field-value\" id=\"result-1\"><\/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=\"59532\" 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\">1<\/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>Atomic Mass 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\\[ A=Z+N,\\qquad m_{\\mathrm{est}}\\approx (Z+N)\\,\\mathrm{u} \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(A\\) \u2014 mass number, a count with no units<\/li>\n<li>\\(Z\\) \u2014 number of protons<\/li>\n<li>\\(N\\) \u2014 number of neutrons<\/li>\n<li>\\(m_{\\mathrm{est}}\\) \u2014 estimated atomic mass in atomic mass units (amu, also written \\(\\mathrm{u}\\))<\/li>\n<\/ul>\n<p>The calculator adds the proton and neutron counts. This gives the exact mass number and an approximate atomic mass in amu, not a measured isotopic mass.<\/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>Atomic Mass \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> keep the default values of 1 proton and 0 neutrons. These counts describe hydrogen-1.<\/p>\n<p>\\[ A=1+0=1,\\qquad m_{\\mathrm{est}}\\approx 1\\,\\mathrm{u} \\]<\/p>\n<p><strong>Result:<\/strong> the calculator displays 1 amu. Hydrogen-1 has a mass number of 1; its actual neutral-atom mass is approximately 1.007825 amu.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the Atomic Mass Calculator<\/h2>\n<ol>\n<li>Enter the isotope\u2019s proton count in <strong>Number of Protons<\/strong>. This count identifies the element: for example, every carbon atom has 6 protons.<\/li>\n<li>Enter its neutron count in <strong>Number of Neutrons<\/strong>. Isotopes of the same element have different neutron counts.<\/li>\n<li>Read <strong>Atomic Mass (Amu)<\/strong>. The displayed number is the sum of the two counts, interpreted as an approximate mass in amu.<\/li>\n<\/ol>\n<p>Use whole, nonnegative counts. Although the fields accept zero, an atom of a chemical element must have at least one proton. If you know an isotope\u2019s notation, its mass number is the number after its name, as in carbon-14; subtract the proton count to find its neutron count.<\/p>\n<h2>What the Result Means<\/h2>\n<p>An atom\u2019s nucleus contains protons and neutrons. Their combined count is its <strong>mass number<\/strong>, usually written \\(A\\). For example, carbon-14 has 6 protons and 8 neutrons, so its mass number is 14. The proton count determines which element it is, while the neutron count distinguishes its isotope. Changing the neutron count changes the calculator\u2019s result without changing the element.<\/p>\n<p>Because a proton and a neutron each have a mass close to one atomic mass unit, the mass number provides a quick estimate of an atom\u2019s mass in amu. An atomic mass unit, or unified atomic mass unit (\\(\\mathrm{u}\\)), is defined as one-twelfth of the mass of a neutral carbon-12 atom. Thus, carbon-12 has an atomic mass of exactly 12 u by definition. For other isotopes, the numerical value of the atomic mass is generally close to\u2014but not exactly equal to\u2014the mass number.<\/p>\n<p>The calculator\u2019s label, <strong>Atomic Mass (Amu)<\/strong>, refers to this estimate. The result is not the <strong>standard atomic weight<\/strong> commonly shown on a periodic table. That value accounts for the masses and relative abundances of an element\u2019s naturally occurring isotopes. This calculator asks only for proton and neutron counts; it does not accept isotope masses or abundances and cannot calculate their weighted average.<\/p>\n<h2>Assumptions and Practical Limits<\/h2>\n<p>Adding protons and neutrons treats each nucleon as contributing about 1 amu. A precise isotopic mass also reflects the masses of electrons and the energy associated with nuclear binding. Those effects explain why most actual atomic masses differ from the integer displayed here. Use a measured isotopic mass when a calculation requires high precision.<\/p>\n<p>Enter counts for <em>one isotope<\/em>, not for a mixture of isotopes or a whole molecule. For instance, entering 6 protons and 8 neutrons estimates the mass of one carbon-14 atom as 14 amu; it does not give the average mass of naturally occurring carbon. Likewise, adding counts from several atoms would not give a precise molecular mass. For calculations involving molecules, see the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/molecular-mass-using-gmv-law\/\">Molecular Mass (GMV Law) calculator<\/a>.<\/p>\n<p>Atomic mass in amu describes the mass of a single atom or isotope on an atomic scale. Molar mass describes the mass of a mole of particles in grams per mole. Their numerical values can be similar for a specified isotope, but their units and uses differ. If you need to relate a number of atoms to moles, use the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/convert-atoms-to-moles\/\">Convert Atoms to Moles calculator<\/a>; the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/avogadros-number\/\">Avogadro\u2019s Number calculator<\/a> provides another way to work with particle counts.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Estimate an isotope\u2019s atomic mass from its numbers of protons and neutrons. Enter the two counts to get an approximate result in atomic mass units (amu).<\/p>\n","protected":false},"author":70,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[54],"tags":[56],"class_list":["post-59532","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\/59532","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\/70"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=59532"}],"version-history":[{"count":4,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/59532\/revisions"}],"predecessor-version":[{"id":65394,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/59532\/revisions\/65394"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=59532"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=59532"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=59532"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}