{"id":64499,"date":"2025-05-12T09:52:19","date_gmt":"2025-05-12T06:52:19","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=64499"},"modified":"2026-10-13T12:13:00","modified_gmt":"2026-10-13T09:13:00","slug":"microstrip-pcb-impedance","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/engineering\/microstrip-pcb-impedance\/","title":{"rendered":"Microstrip PCB Impedance 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\">PCB Trace Impedance Estimator<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"64499\" data-favorite-title=\"Microstrip PCB Impedance\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/engineering\/microstrip-pcb-impedance\/\" data-favorite-excerpt=\"Calculate the characteristic impedance of a microstrip PCB trace from the substrate&#039;s dielectric constant, trace width, substrate height, and copper thickness. Essential for controlled-impedance routing in high-speed and RF designs.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-engineering\">\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\/microstrip-pcb-impedance\/\" method=\"POST\" class=\"calculator\" id=\"calculator-64499\" data-post=\"64499\"><fieldset class=\"fieldset-input\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field has-term\" id=\"input-1\"><label for=\"field-1\">Dielectric constant (\u03b5r)<\/label><div class=\"term\">\u03b5\u1d63<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"dielectric_constant_r\" id=\"field-1\" aria-describedby=\"calc-info-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"1\" value=\"4.5\"\/><small id=\"calc-info-1\">Relative permittivity of PCB substrate<\/small><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-2\">Trace width (W)<\/label><div class=\"term\">W<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"trace_width_w\" id=\"field-2\" aria-describedby=\"calc-unit-2 calc-info-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0.01\" value=\"1\"\/><div class=\"unit\" id=\"calc-unit-2\">mm<\/div><small id=\"calc-info-2\">Width of the microstrip trace<\/small><\/div><div class=\"field has-term\" id=\"input-3\"><label for=\"field-3\">Substrate height (H)<\/label><div class=\"term\">H<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"substrate_height_h\" id=\"field-3\" aria-describedby=\"calc-unit-3 calc-info-3\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0.01\" value=\"1.6\"\/><div class=\"unit\" id=\"calc-unit-3\">mm<\/div><small id=\"calc-info-3\">Height from trace to ground plane<\/small><\/div><div class=\"field has-term\" id=\"input-4\"><label for=\"field-4\">Copper thickness (T)<\/label><div class=\"term\">T<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"copper_thickness_t\" id=\"field-4\" aria-describedby=\"calc-unit-4 calc-info-4\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0\" value=\"0.035\"\/><div class=\"unit\" id=\"calc-unit-4\">mm<\/div><small id=\"calc-info-4\">Thickness of the copper trace<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"64499\">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>Characteristic Impedance<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"\u03a9\"><\/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=\"64499\" 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>Microstrip PCB Impedance 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\\[ Z_0 = \\frac{87}{\\sqrt{\\varepsilon_r + 1.41}} \\cdot \\ln\\left( \\frac{5.98H}{0.8W + T} \\right) \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(Z_0\\) \u2014 characteristic impedance of the microstrip trace (\u03a9)<\/li>\n<li>\\(\\varepsilon_r\\) \u2014 relative dielectric constant (permittivity) of the substrate<\/li>\n<li>\\(W\\) \u2014 trace width (mm)<\/li>\n<li>\\(H\\) \u2014 substrate height, i.e. the distance from the trace to the ground plane (mm)<\/li>\n<li>\\(T\\) \u2014 copper trace thickness (mm)<\/li>\n<\/ul>\n<p>This formula is a widely used closed-form approximation for a single microstrip line on a PCB. It accounts for the finite copper thickness, which effectively widens the trace and lowers the impedance.<\/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>Microstrip PCB Impedance \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> a standard 1.6&nbsp;mm FR-4 board (\\(\\varepsilon_r = 4.5\\)) with a 1&nbsp;mm wide trace and 35&nbsp;\u00b5m (1&nbsp;oz) copper.<\/p>\n<p>\\[ Z_0 = \\frac{87}{\\sqrt{4.5 + 1.41}} \\cdot \\ln\\left( \\frac{5.98 \\times 1.6}{0.8 \\times 1 + 0.035} \\right) \\]<\/p>\n<p>\\[ Z_0 = \\frac{87}{\\sqrt{5.91}} \\cdot \\ln\\left( \\frac{9.568}{0.835} \\right) = \\frac{87}{2.431} \\cdot \\ln(11.459) = 35.78 \\times 2.439 \\approx 87.27~\\Omega \\]<\/p>\n<p><strong>Result:<\/strong> the characteristic impedance is approximately <strong>87.3&nbsp;\u03a9<\/strong>.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to use the calculator<\/h2>\n<ol>\n<li>Enter the <strong>Dielectric constant (\u03b5r)<\/strong> of your substrate \u2014 4.4\u20134.7 for FR-4, around 3.0 for Rogers RO4350B, 2.1\u20132.2 for PTFE-based laminates.<\/li>\n<li>Enter the <strong>Trace width (W)<\/strong> in millimetres. This is the width of the copper trace on the signal layer.<\/li>\n<li>Enter the <strong>Substrate height (H)<\/strong> in millimetres \u2014 the thickness of the dielectric between the trace and the ground plane, not the total board thickness.<\/li>\n<li>Enter the <strong>Copper thickness (T)<\/strong> in millimetres \u2014 0.035&nbsp;mm for 1&nbsp;oz copper, 0.070&nbsp;mm for 2&nbsp;oz copper.<\/li>\n<li>Read the <strong>Characteristic Impedance<\/strong> in ohms. Adjust the trace width and recalculate until you hit your target impedance.<\/li>\n<\/ol>\n<h2>What is microstrip impedance?<\/h2>\n<p>A microstrip is a flat conducting trace routed on an outer PCB layer, with a solid ground plane on the layer beneath it separated by dielectric material. This geometry behaves like a transmission line, and every transmission line has a <em>characteristic impedance<\/em> \\(Z_0\\) \u2014 the ratio of voltage to current of a wave travelling along it.<\/p>\n<p>Because part of the field around a microstrip travels through air (\\(\\varepsilon_r \\approx 1\\)) and part through the substrate, the effective dielectric constant seen by the trace lies between that of air and that of the laminate. Wider traces lower the impedance, while a thicker substrate or a higher dielectric constant raises it.<\/p>\n<p>Controlled impedance matters whenever the rise time of a signal is short compared to the trace's propagation delay \u2014 typically in USB, HDMI, Ethernet, PCIe, DDR memory, and RF circuits. If the trace impedance does not match the driver and receiver (commonly 50&nbsp;\u03a9 single-ended, 90&nbsp;\u03a9 or 100&nbsp;\u03a9 differential), part of the signal reflects at each discontinuity. These reflections cause ringing, overshoot, timing errors, and increased EMI.<\/p>\n<p>For signals embedded between two reference planes, the geometry is called a stripline rather than a microstrip \u2014 see the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/stripline-impedance\/\">Stripline Impedance Calculator<\/a>. For two coupled traces, use the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/stripline-pcb-differential-impedance\/\">Stripline PCB Differential Impedance Calculator<\/a>.<\/p>\n<h2>Assumptions and limitations<\/h2>\n<ul>\n<li><strong>Closed-form accuracy:<\/strong> the formula is an engineering approximation, typically accurate to a few percent for common geometries. For final sign-off of high-speed or RF designs, verify with a field solver or your fabricator's impedance report.<\/li>\n<li><strong>Zero-thickness approximation improved:<\/strong> the \\(0.8W + T\\) term approximates the effect of copper thickness, assuming a rectangular trace cross-section. Trapezoidal etch profiles from manufacturing are not modelled.<\/li>\n<li><strong>Suitable aspect ratios:<\/strong> the model works best for roughly \\(0.1 &lt; W\/H &lt; 2\\). Very wide or very narrow traces deviate from the approximation.<\/li>\n<li><strong>Homogeneous, isotropic substrate:<\/strong> glass-weave inhomogeneity in FR-4 can shift the local impedance, which matters for very high frequencies.<\/li>\n<li><strong>No solder mask:<\/strong> solder mask over the trace slightly lowers the impedance (typically a few ohms). Many fabricators account for this; some designs leave controlled-impedance traces unmasked.<\/li>\n<li><strong>Trace over a solid plane:<\/strong> the ground plane must be continuous and unbroken beneath the trace. Gaps or splits in the plane invalidate the calculation and create impedance discontinuities.<\/li>\n<\/ul>\n<h2>Practical tips<\/h2>\n<ul>\n<li>To <strong>lower<\/strong> the impedance, widen the trace, thin the dielectric, or use a higher-\\(\\varepsilon_r\\) material; to <strong>raise<\/strong> it, do the opposite.<\/li>\n<li>For a 50&nbsp;\u03a9 target on standard 1.6&nbsp;mm FR-4 with 1&nbsp;oz copper, you need roughly a 3&nbsp;mm wide trace \u2014 often impractical, which is why 50&nbsp;\u03a9 designs typically use thinner dielectrics (e.g. 0.2&nbsp;mm prepreg) with ~0.35\u20130.4&nbsp;mm traces.<\/li>\n<li>Keep controlled-impedance traces at a consistent width along their entire length; every via, bend, or layer change introduces a discontinuity.<\/li>\n<li>If you need to couple energy between adjacent traces, estimate the coupling with the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/pcb-microstrip-crosstalk\/\">PCB Microstrip Crosstalk Calculator<\/a>, and match sources to lines with the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/pi-network-impedance-matching\/\">PI Network Impedance Matching Calculator<\/a>.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the characteristic impedance of a microstrip PCB trace from the substrate's dielectric constant, trace width, substrate height, and copper thickness. Essential for controlled-impedance routing in high-speed and RF designs.<\/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":[92],"class_list":["post-64499","post","type-post","status-publish","format-standard","hentry","category-engineering","tag-rf-microwave"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64499","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=64499"}],"version-history":[{"count":6,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64499\/revisions"}],"predecessor-version":[{"id":67108,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64499\/revisions\/67108"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=64499"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=64499"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=64499"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}