{"id":64428,"date":"2025-05-12T09:17:36","date_gmt":"2025-05-12T06:17:36","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=64428"},"modified":"2026-09-30T18:24:15","modified_gmt":"2026-09-30T15:24:15","slug":"lm317-voltage-resistor","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/engineering\/lm317-voltage-resistor\/","title":{"rendered":"LM317 Voltage and Resistor 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\">Adjustable Voltage Regulator Output Tool<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"64428\" data-favorite-title=\"LM317 Voltage and Resistor\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/engineering\/lm317-voltage-resistor\/\" data-favorite-excerpt=\"Calculate the LM317 output voltage from resistors R1 and R2, or find the resistor values for a target voltage. Enter the two resistances to get the regulated output in volts.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-electrical\">\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\/engineering\/lm317-voltage-resistor\/\" method=\"POST\" class=\"calculator\" id=\"calculator-64428\" data-post=\"64428\"><fieldset class=\"fieldset-input\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field has-term\" id=\"input-1\"><label for=\"field-1\">Resistor R1<\/label><div class=\"term\">R1<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"resistor_r1\" id=\"field-1\" aria-describedby=\"calc-unit-1 calc-info-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0.1\" value=\"240\"\/><div class=\"unit\" id=\"calc-unit-1\">\u03a9<\/div><small id=\"calc-info-1\">Resistor connected between output and adjust pin<\/small><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-2\">Resistor R2<\/label><div class=\"term\">R2<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"resistor_r2\" id=\"field-2\" aria-describedby=\"calc-unit-2 calc-info-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0.1\" value=\"1200\"\/><div class=\"unit\" id=\"calc-unit-2\">\u03a9<\/div><small id=\"calc-info-2\">Resistor between adjust pin and ground<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"64428\">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>Output Voltage<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"V\"><\/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=\"64428\" 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\">1<\/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>LM317 Output Voltage 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\\[ V_{out} = V_{ref} \\cdot \\left(1 + \\frac{R2}{R1}\\right) + I_{adj} \\cdot R2 \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(V_{out}\\) \u2014 output voltage (V)<\/li>\n<li>\\(V_{ref}\\) \u2014 internal reference voltage, \\(1.25\\text{ V}\\) for the LM317<\/li>\n<li>\\(R1\\) \u2014 resistor between the output and adjust pins (\u03a9)<\/li>\n<li>\\(R2\\) \u2014 resistor between the adjust pin and ground (\u03a9)<\/li>\n<li>\\(I_{adj}\\) \u2014 adjust pin current, typically \\(50\\text{ \u00b5A}\\)<\/li>\n<\/ul>\n<p>The LM317 holds a fixed \\(1.25\\text{ V}\\) across \\(R1\\), which sets a constant current through the resistor divider; the output voltage is the reference voltage plus the drop across \\(R2\\).<\/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>LM317 Voltage \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> an LM317 regulator uses the standard resistor values \\(R1 = 240\\ \\Omega\\) and \\(R2 = 1200\\ \\Omega\\).<\/p>\n<p>\\[ V_{out} = 1.25 \\cdot \\left(1 + \\frac{1200}{240}\\right) + 0.00005 \\cdot 1200 \\]<\/p>\n<p>\\[ V_{out} = 1.25 \\cdot 6 + 0.06 = 7.5 + 0.06 = 7.56\\ \\text{V} \\]<\/p>\n<p><strong>Result:<\/strong> the output voltage is approximately <strong>7.56 V<\/strong>. Ignoring the small adjust pin current gives \\(7.5\\text{ V}\\), the value most datasheets quote for this classic resistor pair.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the LM317 Calculator<\/h2>\n<ol>\n<li>Enter the value of <strong>Resistor R1<\/strong> in ohms. This is the resistor connected between the output and adjust pins; 240 \u03a9 is the datasheet recommendation.<\/li>\n<li>Enter the value of <strong>Resistor R2<\/strong> in ohms. This resistor sits between the adjust pin and ground.<\/li>\n<li>Read the <strong>Output Voltage<\/strong> in volts, calculated with \\(V_{ref} = 1.25\\text{ V}\\) and \\(I_{adj} = 50\\text{ \u00b5A}\\).<\/li>\n<\/ol>\n<p>To find an \\(R2\\) value for a desired output voltage, rearrange the formula and solve for \\(R2\\), then use the calculator to verify the result:<\/p>\n<p>\\[ R2 = R1 \\cdot \\frac{V_{out} - V_{ref}}{V_{ref} + I_{adj} \\cdot R1} \\]<\/p>\n<h2>About the LM317 Adjustable Regulator<\/h2>\n<p>The LM317 is one of the most popular linear voltage regulators ever made. Unlike fixed 5 V or 12 V regulators, its output can be set anywhere from \\(1.25\\text{ V}\\) up to about \\(37\\text{ V}\\) simply by choosing two resistors. It requires an input voltage at least \\(2\\text{ V}\\) to \\(3\\text{ V}\\) above the desired output (the dropout voltage), and it can supply up to 1.5 A with adequate heatsinking.<\/p>\n<p>The device works by maintaining exactly \\(1.25\\text{ V}\\) between its output and adjust pins. This constant voltage across \\(R1\\) drives a fixed current through the divider, and the regulator raises its output until the voltage at the adjust pin matches what the divider produces. Because the feedback loop closes through the divider, the output is stable and predictable once the resistor ratio is fixed.<\/p>\n<p>In practice, the \\(I_{adj} \\cdot R2\\) term contributes only a few tens of millivolts and is often neglected for quick estimates. However, the adjust pin current is not perfectly constant, so where precision matters \u2014 or when \\(R2\\) is large \u2014 keeping the full formula avoids surprises. For most hobby and general-purpose supplies, the simplified formula \\(V_{out} \\approx 1.25 (1 + R2\/R1)\\) is accurate to within about 1%.<\/p>\n<p>Typical applications include bench power supplies, battery chargers, LED drivers with current-limiting configurations, and adjustable bias supplies. If you need a fixed reference or a shunt-style regulator, a <a href=\"https:\/\/wpcalc.com\/en\/engineering\/zener-diode\/\">Zener diode resistor calculator<\/a> covers a different but related design approach.<\/p>\n<h2>Choosing Resistor Values \u2014 Tips and Limitations<\/h2>\n<ul>\n<li><strong>Keep R1 near 240 \u03a9.<\/strong> The datasheet recommends \\(R1 = 240\\ \\Omega\\) so that the divider current (about 5 mA) is large enough to keep the regulator in stable operation; the LM317 needs a minimum load current of typically 3.5\u201310 mA.<\/li>\n<li><strong>Use standard values.<\/strong> Because resistor tolerance directly affects output accuracy, 1% metal-film resistors give noticeably better results than 5% carbon types. If you need an odd value, combine resistors and check the equivalent with a <a href=\"https:\/\/wpcalc.com\/en\/engineering\/parallel-resistance\/\">parallel resistance calculator<\/a>.<\/li>\n<li><strong>Respect the input-output headroom.<\/strong> The input voltage must exceed the output by at least the dropout voltage (2\u20133 V). Above that, the regulator dissipates \\((V_{in} - V_{out}) \\cdot I_{load}\\) as heat \u2014 size the heatsink accordingly.<\/li>\n<li><strong>Watch the dissipation in R2.<\/strong> At high output voltages \\(R2\\) can dissipate meaningful power; check that its wattage rating is adequate.<\/li>\n<li><strong>Add bypass capacitors.<\/strong> An input capacitor (0.1 \u00b5F) and an output capacitor (1 \u00b5F tantalum or 10 \u00b5F electrolytic) improve transient response and stability; an optional 10 \u00b5F capacitor across \\(R2\\) boosts ripple rejection.<\/li>\n<li><strong>Current flowing to the load also flows through your wiring.<\/strong> For higher currents, verify conductor sizing with a <a href=\"https:\/\/wpcalc.com\/en\/engineering\/wire-gauge\/\">wire gauge calculator<\/a> to limit voltage drop and heating.<\/li>\n<\/ul>\n<p>The calculator assumes typical datasheet values of \\(V_{ref} = 1.25\\text{ V}\\) and \\(I_{adj} = 50\\text{ \u00b5A}\\). Actual devices vary slightly between units, so measure the real output voltage after building the circuit and fine-tune \\(R2\\) with a trimmer if you need tighter accuracy.<\/p>\n<h2>Common R1\/R2 Combinations (R1 = 240 \u03a9)<\/h2>\n<table>\n<thead>\n<tr>\n<th>R2<\/th>\n<th>Vout (approx.)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>240 \u03a9<\/td>\n<td>2.5 V<\/td>\n<\/tr>\n<tr>\n<td>720 \u03a9<\/td>\n<td>5.0 V<\/td>\n<\/tr>\n<tr>\n<td>1.2 k\u03a9<\/td>\n<td>7.5 V<\/td>\n<\/tr>\n<tr>\n<td>2.16 k\u03a9<\/td>\n<td>12.5 V<\/td>\n<\/tr>\n<tr>\n<td>3.36 k\u03a9<\/td>\n<td>18.8 V<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Values are computed with the simplified formula; the full calculation adds roughly \\(I_{adj} \\cdot R2\\) to each result.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the LM317 output voltage from resistors R1 and R2, or find the resistor values for a target voltage. Enter the two resistances to get the regulated output in volts.<\/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":[4],"tags":[94],"class_list":["post-64428","post","type-post","status-publish","format-standard","hentry","category-engineering","tag-circuits"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64428","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=64428"}],"version-history":[{"count":3,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64428\/revisions"}],"predecessor-version":[{"id":65984,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64428\/revisions\/65984"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=64428"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=64428"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=64428"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}