{"id":60610,"date":"2016-01-16T11:06:58","date_gmt":"2016-01-16T09:06:58","guid":{"rendered":"https:\/\/wpcalc.com\/?p=60610"},"modified":"2026-09-28T14:06:28","modified_gmt":"2026-09-28T11:06:28","slug":"ultrasound-gestation-period","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/pregnancy-baby\/ultrasound-gestation-period\/","title":{"rendered":"Ultrasound Gestation Period 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\">Gestational Age Estimator by Ultrasound Data<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"60610\" data-favorite-title=\"Ultrasound Gestation Period\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/ultrasound-gestation-period\/\" data-favorite-excerpt=\"Enter an ultrasound crown\u2013rump length of 3\u201384 mm to estimate gestational age in weeks and days. The result is an approximate pregnancy term, not a clinical dating assessment.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-embryo\">\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\/pregnancy-baby\/ultrasound-gestation-period\/\" method=\"POST\" class=\"calculator\" id=\"calculator-60610\" data-post=\"60610\"><fieldset class=\"fieldset-input\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field\" id=\"input-1\"><label for=\"field-1\">Embryo length, mm<\/label><input type=\"text\" name=\"embryo_length_mm\" id=\"field-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"3\" max=\"84\" value=\"25\"\/><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"60610\">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>Pregnancy term<\/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=\"60610\" 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\">1<\/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>Ultrasound Gestation Period 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 = 6.5 + 0.15L \\]\n\\[ T = \\operatorname{round}(7A) \\]\n\\[ W = \\left\\lfloor T\/7 \\right\\rfloor, \\qquad d = T \\bmod 7 \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(L\\) \u2014 embryo crown\u2013rump length (CRL) in millimeters.<\/li>\n<li>\\(A\\) \u2014 estimated gestational age in weeks before rounding.<\/li>\n<li>\\(T\\) \u2014 estimated gestational age rounded to a whole number of days.<\/li>\n<li>\\(W\\) and \\(d\\) \u2014 completed weeks and additional days shown in the result.<\/li>\n<\/ul>\n<p>The calculator applies a simplified linear estimate to the entered length, then converts it to weeks and days. This equation is the one used by this calculator; clinical ultrasound dating may use different equations or reference charts.<\/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>Ultrasound Gestation Period \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> an ultrasound report gives an embryo crown\u2013rump length of 25 mm.<\/p>\n<p>\\[ A = 6.5 + 0.15(25) = 10.25\\text{ weeks} \\]<\/p>\n<p>\\[ T = \\operatorname{round}(10.25 \\times 7) = \\operatorname{round}(71.75) = 72\\text{ days} \\]<\/p>\n<p>\\[ 72\\text{ days} = 10\\text{ weeks} + 2\\text{ days} \\]<\/p>\n<p><strong>Result:<\/strong> an estimated pregnancy term of 10 weeks 2 days.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to use the calculator<\/h2>\n<ol>\n<li>Find the crown\u2013rump length (CRL) on your ultrasound report. This is the measurement from the top of the embryo or fetus\u2019s head to its bottom, excluding the legs. The report may abbreviate it as \u201cCRL.\u201d<\/li>\n<li>Enter that measurement in the <strong>Embryo length, mm<\/strong> field. Use millimeters: for example, enter 25 if the report says 25 mm, or 25 if it says 2.5 cm.<\/li>\n<li>Read the <strong>Pregnancy term<\/strong> result as completed weeks plus additional days. An entry of 25 mm produces 10 weeks 2 days.<\/li>\n<\/ol>\n<p>The accepted input range is 3\u201384 mm, and decimal measurements are allowed. An entry outside that range produces an error rather than a pregnancy-term estimate. The calculator has no field for a last menstrual period, ultrasound date, or estimated due date.<\/p>\n<h2>What an ultrasound gestation estimate means<\/h2>\n<p>Gestational age describes how far along a pregnancy is. It is conventionally counted from the first day of the last menstrual period, rather than from fertilization, which typically happens about two weeks later. Thus, a result of 10 weeks 2 days is a gestational-age estimate, not a claim that conception occurred 10 weeks and 2 days ago.<\/p>\n<p>In early pregnancy, a sonographer can measure CRL to help date a pregnancy. A clinician interprets that measurement alongside the scan date, the quality of the image, and any established pregnancy dating. CRL is not the same as gestational-sac diameter, biparietal diameter (BPD), or femur length (FL). Do not enter one of those other measurements here simply because it is also reported in millimeters. For more on the measurement itself, see the <a href=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/crown-rump-length\/\">Crown Rump Length (CRL) calculator<\/a>.<\/p>\n<p>Weeks-and-days notation can make estimates easier to compare with a prenatal schedule, but it does not make them exact. If you need to compare a date-based estimate, the <a href=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/gestational-age\/\">Gestational Age Calculator (AOG)<\/a> and <a href=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/how-many-weeks-pregnant\/\">How Many Weeks Pregnant Are You?<\/a> use different starting information. Their answers may not match this length-based result.<\/p>\n<h2>Assumptions and limitations<\/h2>\n<p>This calculator uses the fixed equation \\(A=6.5+0.15L\\) throughout its entire accepted range. Real CRL growth does not follow one straight-line relationship across all early-pregnancy measurements. As a result, the displayed term can differ substantially from an ultrasound report, particularly at larger CRL values. An accepted input is not a guarantee that the resulting age is clinically reliable.<\/p>\n<ul>\n<li><strong>Check the measurement:<\/strong> use a reported CRL, not an estimated overall fetal length or a value taken from another ultrasound measurement.<\/li>\n<li><strong>Check the units:<\/strong> convert centimeters to millimeters before entering the number; 1 cm equals 10 mm.<\/li>\n<li><strong>Allow for uncertainty:<\/strong> image quality, measurement technique, and the dating method all affect estimates. The calculator rounds its computed age to the nearest whole day.<\/li>\n<li><strong>Use your clinical dating for decisions:<\/strong> if this result conflicts with your ultrasound report or your clinician\u2019s estimated gestational age, ask your prenatal care professional which date to use.<\/li>\n<\/ul>\n<p>To explore an estimated delivery date once your pregnancy dating has been established, use the <a href=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/pregnancy-due-date\/\">Pregnancy Due Date calculator<\/a>. A due date is itself an estimate and should not be inferred from this calculator\u2019s output without knowing when the ultrasound measurement was taken.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Enter an ultrasound crown\u2013rump length of 3\u201384 mm to estimate gestational age in weeks and days. The result is an approximate pregnancy term, not a clinical dating assessment.<\/p>\n","protected":false},"author":70,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[45],"tags":[47],"class_list":["post-60610","post","type-post","status-publish","format-standard","hentry","category-pregnancy-baby","tag-pregnancy-tracking"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/60610","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=60610"}],"version-history":[{"count":3,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/60610\/revisions"}],"predecessor-version":[{"id":65390,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/60610\/revisions\/65390"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=60610"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=60610"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=60610"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}