{"id":67331,"date":"2026-10-21T09:55:01","date_gmt":"2026-10-21T06:55:01","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=67331"},"modified":"2026-10-21T09:55:01","modified_gmt":"2026-10-21T06:55:01","slug":"mm-to-inches-converter","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/converters\/mm-to-inches-converter\/","title":{"rendered":"mm to Inches Converter"},"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\">Convert Millimeters to Inches \u2014 and Inches Back to Millimeters<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"67331\" data-favorite-title=\"mm to Inches\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/converters\/mm-to-inches-converter\/\" data-favorite-excerpt=\"Convert millimeters to inches and back in one step, with the exact decimal result plus the nearest fractional inch (down to 1\/64 in) and the rounding error. Just type your value in either field.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-length\">\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\/converters\/mm-to-inches-converter\/\" method=\"POST\" class=\"calculator\" id=\"calculator-67331\" data-post=\"67331\"><fieldset class=\"fieldset-input is-2\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field has-term\" id=\"input-1\"><label for=\"field-1\">Millimeters (mm)<\/label><div class=\"term\">mm<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"millimeters_mm\" id=\"field-1\" aria-describedby=\"calc-unit-1 calc-info-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0\" value=\"25\"\/><div class=\"unit\" id=\"calc-unit-1\">mm<\/div><small id=\"calc-info-1\">Type in either field \u2014 the converter follows the field you last edited.<\/small><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-2\">Inches (in)<\/label><div class=\"term\">in<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"inches_in\" id=\"field-2\" aria-describedby=\"calc-unit-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0\" value=\"0.98425\"\/><div class=\"unit\" id=\"calc-unit-2\">in<\/div><\/div><div class=\"field is-single\" id=\"input-3\"><label for=\"field-3\">Fractional-inch precision<\/label><div class=\"grid grid-cols-1\"><select id=\"field-3\" name=\"fractionalinch_precision\"><option value=\"8\">1\/8 in<\/option><option value=\"16\">1\/16 in<\/option><option value=\"32\">1\/32 in<\/option><option value=\"64\" selected>1\/64 in<\/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><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"67331\">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> Conversion Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Millimeters<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"mm\"><\/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>Inches (exact)<\/span><\/span><span class=\"field-value\" id=\"result-2\" data-unit=\"in\"><\/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-3\"><span class=\"field-title\"><span>Inches, nearest fraction<\/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 class=\"field-result\" id=\"output-4\"><span class=\"field-title\"><span>Fraction rounding error (frac \u2212 exact)<\/span><\/span><span class=\"field-value\" id=\"result-4\"><\/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-5\"><span class=\"field-title\"><span>Formula with your values<\/span><\/span><span class=\"field-value\" id=\"result-5\"><\/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-6\"><span class=\"field-title\"><span>Conversion table: 1\u2013100 mm in inches<\/span><\/span><span class=\"field-value\" id=\"result-6\"><\/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-7\"><span class=\"field-title\"><span>Machinist&#039;s chart: fractional inches 1\/64\u20131 in in mm<\/span><\/span><span class=\"field-value\" id=\"result-7\"><\/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-8\"><span class=\"field-title\"><span>Common drill bit and wrench sizes in mm and inches<\/span><\/span><span class=\"field-value\" id=\"result-8\"><\/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=\"67331\" 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>mm to Inches 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\\[ \\text{inches} = \\frac{\\text{millimeters}}{25.4} \\\\ \\text{millimeters} = \\text{inches} \\times 25.4 \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(\\text{millimeters}\\) \u2014 length in mm<\/li>\n<li>\\(\\text{inches}\\) \u2014 the same length in inches<\/li>\n<li>\\(25.4\\) \u2014 the exact number of millimeters in one inch<\/li>\n<\/ul>\n<p>Both formulas are exact, because the inch has been defined as exactly 25.4 mm by international agreement since 1959.<\/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>mm to Inches \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> you measure a bolt shaft as 25 mm long and need to express it in inches, including the nearest 1\/64-inch fraction.<\/p>\n<p>\\[ 25 \\div 25.4 = 0.984252 \\text{ in} \\]<\/p>\n<p>Then round to the nearest 1\/64 in: \\(0.984252 \\times 64 \\approx 63\\), so 25 mm \u2248 63\/64 in (0.984375 in).<\/p>\n<p><strong>Result:<\/strong> 25 mm = 0.984252 in exactly = 63\/64 in to 1\/64 precision; the fraction overshoots the exact value by about +0.000123 in (+0.00313 mm).<\/p>\n<p>\n\r\n<\/section>\n<h2>How to use the calculator<\/h2>\n<ol>\n<li>Type your length into the <strong>Millimeters (mm)<\/strong> field or the <strong>Inches (in)<\/strong> field \u2014 the converter follows whichever field you edited last and fills in the other one automatically.<\/li>\n<li>Set <strong>Fractional-inch precision<\/strong> to 1\/8, 1\/16, 1\/32 or 1\/64 in to control how the fractional-inch result and its rounding error are rounded.<\/li>\n<li>Read the <strong>Conversion Results<\/strong>: the value in both units, the exact inches, the nearest fraction (e.g. 63\/64 in instead of 0.984252 in), and how far the fraction is from the exact decimal.<\/li>\n<li>Scroll down for the ready-made tables: mm 1\u2013100 in inches, fractional inches 1\/64\u20131 in in mm, and common drill bit and wrench sizes in both systems.<\/li>\n<\/ol>\n<h2>Millimeters and inches explained<\/h2>\n<p>The millimeter belongs to the metric system and the inch to the imperial\/US customary system, so drawings, tools and parts from different countries often mix the two. The link between them is fixed by definition: one inch equals 25.4 mm exactly. That makes conversion a simple multiplication or division with no hidden rounding \u2014 dividing by 25.4 takes you from mm to inches, multiplying by 25.4 takes you back.<\/p>\n<p>The decimal result is the mathematically exact answer, and the calculator shows it with up to six decimal places. In practice \u2014 machining, woodworking, construction \u2014 lengths are often given in fractional inches instead, because rulers, tapes and calipers in inch countries are graduated in fractions such as 1\/8, 1\/16 or 1\/64 in. That is why the tool also reports the <em>nearest fraction<\/em> at your chosen precision.<\/p>\n<p>The <strong>fraction rounding error<\/strong> tells you how much you give up by using the fraction instead of the exact decimal. In the default example, 63\/64 in is 0.000123 in (about 3 micrometers) longer than the true value of 25 mm \u2014 negligible for woodworking, but possibly significant in precision machining. If the error exceeds your tolerance, switch to a finer precision (e.g. from 1\/8 to 1\/64) or work with the decimal figure directly.<\/p>\n<p>For everyday reference: 1 mm \u2248 0.03937 in, 10 mm \u2248 0.3937 in (close to 25\/64 in), 25 mm \u2248 1 in minus a hair, and 100 mm \u2248 3.937 in. Working in the <a href=\"https:\/\/wpcalc.com\/en\/converters\/cm-to-inches-converter\/\">cm to inches converter<\/a> can be handier for longer measurements; for heights and room dimensions see the <a href=\"https:\/\/wpcalc.com\/en\/converters\/feet-and-inches-calculator\/\">feet and inches calculator<\/a> or the <a href=\"https:\/\/wpcalc.com\/en\/converters\/meters-to-feet\/\">meters to feet converter<\/a>.<\/p>\n<h2>Assumptions, limitations and practical tips<\/h2>\n<ul>\n<li><strong>Exact factor:<\/strong> all results use 1 in = 25.4 mm exactly (international yard and pound agreement, 1959). Older US survey units differ minutely; for everyday work this is irrelevant.<\/li>\n<li><strong>Non-negative lengths only:<\/strong> the tool accepts values from 0 up to 1,000,000,000 mm (about 393.7 miles) or 40,000,000 inches.<\/li>\n<li><strong>Two-way field:<\/strong> the converter tracks which field you edited last. If both change at once, retype the value in the field you care about to set the direction.<\/li>\n<li><strong>Fractions are approximations:<\/strong> most decimal inch values have no exact fraction, so the nearest fraction almost always carries a small rounding error \u2014 always check it against your tolerance.<\/li>\n<li><strong>Wrench and drill sizes:<\/strong> nominal metric and inch sizes are close but not interchangeable (13 mm vs 1\/2 in = 12.7 mm). Always match the tool to the fastener or drill to the marked job.<\/li>\n<li><strong>Kitchen-variety conversions:<\/strong> when precision matters, prefer the decimal result; when laying out lines with a ruler graduated in fractions, use the nearest-fraction value.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Convert millimeters to inches and back in one step, with the exact decimal result plus the nearest fractional inch (down to 1\/64 in) and the rounding error. Just type your value in either field.<\/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":[3],"tags":[29],"class_list":["post-67331","post","type-post","status-publish","format-standard","hentry","category-converters","tag-length-units"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/67331","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=67331"}],"version-history":[{"count":1,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/67331\/revisions"}],"predecessor-version":[{"id":67332,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/67331\/revisions\/67332"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=67331"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=67331"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=67331"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}