{"id":66744,"date":"2026-10-13T08:52:18","date_gmt":"2026-10-13T05:52:18","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=66744"},"modified":"2026-10-13T08:52:18","modified_gmt":"2026-10-13T05:52:18","slug":"dew-point-calculator","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/converters\/dew-point-calculator\/","title":{"rendered":"Dew Point 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\">Find the Temperature at Which Moisture Starts to Condense<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"66744\" data-favorite-title=\"Dew Point\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/converters\/dew-point-calculator\/\" data-favorite-excerpt=\"Enter the air temperature and relative humidity to find the dew point \u2014 the temperature at which moisture starts to condense. Results include dew point in \u00b0C, \u00b0F and K, vapour pressures and a condensation risk assessment.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-physic\">\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\/dew-point-calculator\/\" method=\"POST\" class=\"calculator\" id=\"calculator-66744\" data-post=\"66744\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field has-term\" id=\"input-1\"><label for=\"field-1\">Air temperature (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><div class=\"field-group\"><input type=\"number\" name=\"air_temperature_t\" id=\"field-1\" aria-describedby=\"calc-info-1\" placeholder=\"e.g. 25\" step=\"any\" value=\"25\"\/><div class=\"grid grid-cols-1\"><select id=\"field-2\" name=\"unit\" aria-label=\"Unit\"><option value=\"c\" selected>\u00b0C<\/option><option value=\"f\">\u00b0F<\/option><option value=\"k\">K<\/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><small id=\"calc-info-1\">Temperature of the surrounding air.<\/small><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-3\">Relative humidity (RH)<\/label><div class=\"term\">RH<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"relative_humidity_rh\" id=\"field-3\" aria-describedby=\"calc-unit-3 calc-info-3\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 60\" min=\"0\" max=\"100\" value=\"60\"\/><div class=\"unit\" id=\"calc-unit-3\">%<\/div><small id=\"calc-info-3\">Percentage of water vapour in the air relative to the maximum it can hold at this temperature (0\u2013100 %).<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"66744\">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> Dew Point Results<\/h3><div class=\"result-box\"><div class=\"field-result is-column\" id=\"output-1\"><span class=\"field-title\"><span>Dew point temperature (Td)<\/span><span class=\"result-term\">Td<\/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 class=\"field-result is-column\" id=\"output-2\"><span class=\"field-title\"><span>Water vapour pressures and condensation risk<\/span><\/span><span class=\"field-value\" id=\"result-2\"><\/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=\"66744\" 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>Dew Point 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\\[ \\gamma = \\ln\\!\\left(\\frac{RH}{100}\\right) + \\frac{a \\, T}{b + T} \\qquad T_d = \\frac{b \\, \\gamma}{a - \\gamma} \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(T\\) \u2014 air temperature (\u00b0C)<\/li>\n<li>\\(RH\\) \u2014 relative humidity (%)<\/li>\n<li>\\(T_d\\) \u2014 dew point temperature (\u00b0C)<\/li>\n<li>\\(a = 17.625\\) and \\(b = 243.04\\,\\text{\u00b0C}\\) \u2014 constants of the Magnus-Tetens approximation (Alduchov &amp; Eskridge, 1996)<\/li>\n<\/ul>\n<p>This is the Magnus-Tetens formula: it finds the temperature at which the air becomes saturated, using the fact that relative humidity equals the ratio of the actual vapour pressure to the saturation vapour pressure. The related saturation vapour pressure used in the results is \\(e_s = 6.112 \\, \\exp\\!\\left(\\frac{aT}{b+T}\\right)\\) hPa.<\/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>Dew Point \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> the air in a room is 25 \u00b0C with a relative humidity of 60 %. At what temperature does moisture start to condense?<\/p>\n<p>\\[ \\gamma = \\ln\\!\\left(\\frac{60}{100}\\right) + \\frac{17.625 \\times 25}{243.04 + 25} = -0.5108 + 1.6438 = 1.1330 \\]<\/p>\n<p>\\[ T_d = \\frac{243.04 \\times 1.1330}{17.625 - 1.1330} = \\frac{275.37}{16.492} \\approx 16.70 \\,\\text{\u00b0C} \\]<\/p>\n<p><strong>Result:<\/strong> the dew point is <strong>16.70 \u00b0C<\/strong> (62.06 \u00b0F, 289.85 K). Any surface \u2014 a window, a wall, a cold drink \u2014 cooled below this temperature will collect condensation. The dew point spread is 25 \u2212 16.70 = 8.3 \u00b0C, which indicates fairly dry, comfortable air.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the Calculator<\/h2>\n<ol>\n<li>Enter the <strong>Air temperature (T)<\/strong> of the surrounding air.<\/li>\n<li>Pick the matching <strong>Unit<\/strong> \u2014 \u00b0C, \u00b0F or K. The result is converted back into the same unit.<\/li>\n<li>Enter the <strong>Relative humidity (RH)<\/strong> as a percentage between 0 and 100. Many weather apps, hygrometers and HVAC reports show this value directly.<\/li>\n<li>Read the results: the <strong>Dew point temperature (Td)<\/strong> in all three temperature units, plus the vapour pressures, the dew point spread and a short condensation risk assessment.<\/li>\n<\/ol>\n<h2>What Is the Dew Point?<\/h2>\n<p>The dew point is the temperature to which air must be cooled, at constant pressure, for the water vapour in it to become saturated and begin to condense into liquid water \u2014 dew, fog, or droplets on a cold surface. Unlike relative humidity, which changes as the temperature changes, the dew point is a direct measure of how much moisture the air actually holds. Two rooms with very different temperatures but the same dew point contain exactly the same amount of water vapour.<\/p>\n<p>This makes the dew point the most useful single number for judging how muggy or dry the air feels. A dew point below 10 \u00b0C feels dry, 10\u201316 \u00b0C feels comfortable, 16\u201321 \u00b0C noticeably humid, and above 21 \u00b0C most people describe the air as oppressive. Weather forecasts increasingly quote the dew point rather than relative humidity precisely because it maps so cleanly onto perceived comfort.<\/p>\n<p>In practice, the dew point tells you the condensation threshold: moisture will form on any surface whose temperature falls to or below \\(T_d\\). That is why a cold glass of water \"sweats\" in summer, why bathroom mirrors fog up during a shower, and why uninsulated walls and single-glazed windows collect water in winter. The <strong>dew point spread<\/strong> (\\(T - T_d\\)) shown in the results summarises the risk: a spread under 2 \u00b0C means the air is nearly saturated and even slight cooling produces condensation, while a spread above 5 \u00b0C means fairly dry conditions with little condensation risk.<\/p>\n<p>The calculator also reports the saturation vapour pressure at the air temperature, the actual vapour pressure in the air, and the saturation pressure at the dew point. At the dew point the last two are equal \u2014 that is the very definition of saturation, and it is a good consistency check on the result.<\/p>\n<h2>Accuracy, Assumptions and Practical Tips<\/h2>\n<ul>\n<li><strong>Valid temperature range.<\/strong> The Magnus formula with \\(a = 17.625\\), \\(b = 243.04\\) \u00b0C is accurate to within about 0.35 \u00b0C for air temperatures from \u221240 \u00b0C to +50 \u00b0C at normal atmospheric pressure. Outside this range the result is only an approximation, and the calculator will flag it.<\/li>\n<li><strong>One atmosphere assumed.<\/strong> The formula assumes air near standard sea-level pressure. For high altitudes or pressurised spaces the true dew point shifts slightly, but for most everyday purposes the difference is negligible.<\/li>\n<li><strong>Relative humidity must be above 0 %.<\/strong> At exactly 0 % humidity the dew point is undefined (the air contains no water vapour); the calculator requires a value between 0 (exclusive) and 100 %.<\/li>\n<li><strong>Frost point below 0 \u00b0C.<\/strong> When the dew point is below freezing, water vapour in practice deposits directly as frost rather than liquid dew. The true frost point is slightly higher than the computed dew point, and the calculator notes this whenever it applies.<\/li>\n<li><strong>Measuring humidity.<\/strong> Cheap hygrometers can drift by several percentage points; for a reliable dew point, check the sensor against a known reference (for example, saturated salt solutions) and recalibrate if needed.<\/li>\n<li><strong>Condensation inside buildings.<\/strong> To prevent mould and moisture damage, keep indoor surfaces warmer than the dew point \u2014 typically by ventilating, insulating cold bridges (window frames, corners, external walls), and not letting indoor relative humidity climb much above 60 % in cold weather.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Enter the air temperature and relative humidity to find the dew point \u2014 the temperature at which moisture starts to condense. Results include dew point in \u00b0C, \u00b0F and K, vapour pressures and a condensation risk assessment.<\/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":[34],"class_list":["post-66744","post","type-post","status-publish","format-standard","hentry","category-converters","tag-physics-units"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66744","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=66744"}],"version-history":[{"count":1,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66744\/revisions"}],"predecessor-version":[{"id":66745,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66744\/revisions\/66745"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=66744"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=66744"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=66744"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}