{"id":379,"date":"2026-04-02T10:07:00","date_gmt":"2026-04-02T14:07:00","guid":{"rendered":"\/blog\/?p=379"},"modified":"2026-05-10T00:48:28","modified_gmt":"2026-05-10T04:48:28","slug":"gpm-to-lpm-conversion-formula-calculator-us-uk-gallons","status":"publish","type":"post","link":"\/blog\/gpm-to-lpm-conversion-formula-calculator-us-uk-gallons","title":{"rendered":"GPM to LPM Conversion: Formula, Calculator, and Reference Table (US and UK Gallons)"},"content":{"rendered":"\n<p>If you\u2019ve grabbed a flow rate from a US-spec pump and need to compare it to a European product, you\u2019ve hit the GPM-to-LPM problem. The conversion isn\u2019t hard \u2014 it\u2019s a single multiplication \u2014 but <strong>two different gallons<\/strong> are in common use, and most calculators silently assume one of them. Pick the wrong one and your spec is off by ~20%.<\/p>\n\n\n\n<p>This guide gives you the exact formula for both gallon types, a worked example, a reference table covering 0.1 to 1000 GPM, and a quick decision tree for which gallon to use.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Jump to a section<\/h2>\n\n\n\n<ul class=\"wp-block-list\"><li><a href=\"#two-gallons\">The two-gallon problem (and which one to use)<\/a><\/li><li><a href=\"#formula\">The formula<\/a><\/li><li><a href=\"#example\">Worked example: sizing a pool pump<\/a><\/li><li><a href=\"#table\">Quick reference table<\/a><\/li><li><a href=\"#common-rates\">Common pump and plumbing flow rates<\/a><\/li><li><a href=\"#faq\">FAQ<\/a><\/li><\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"two-gallons\">The two-gallon problem (and which one to use)<\/h2>\n\n\n\n<p>There are two \u201cgallons\u201d in everyday engineering use, and they\u2019re meaningfully different:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"table table-hover\"><thead><tr><th>Gallon<\/th><th>Volume<\/th><th>Where it\u2019s used<\/th><\/tr><\/thead><tbody><tr><td><strong>US gallon<\/strong><\/td><td>3.78541 L<\/td><td>United States \u2014 plumbing, irrigation, automotive, residential pumps<\/td><\/tr><tr><td><strong>Imperial \/ UK gallon<\/strong><\/td><td>4.54609 L<\/td><td>United Kingdom, parts of the Caribbean, Canadian fuel economy figures<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>The two differ by roughly <strong>20%<\/strong> (the Imperial gallon is 20.1% larger than the US gallon \u2014 equivalently, the US gallon is 16.7% smaller than the Imperial) \u2014 enough to size a pump wrong if you ignore it. The litre is the same everywhere (defined by SI), so the divergence is entirely on the gallon side.<\/p>\n\n\n\n<p><strong>Which one to use?<\/strong> Almost always the US gallon. Every US-built pump, water meter, and shower head is rated in US GPM. The Imperial gallon shows up mainly in older British equipment specs and Canadian fuel-economy figures. If a spec sheet says \u201cGPM\u201d without qualifying, default to US. If you\u2019re reading a UK plumbing standard or rating an older British pump, switch to Imperial.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"formula\">The formula<\/h2>\n\n\n\n<p>For US gallons (the common case):<\/p>\n\n\n\n<p>For Imperial gallons:<\/p>\n\n\n\n<p>In both cases the \u201cper minute\u201d part stays put \u2014 only the volume unit changes. To go the other way:<\/p>\n\n\n\n<p>xconvert\u2019s <a href=\"https:\/\/www.xconvert.com\/unit-converter\/gallons-per-minute-to-litres-per-minute\">GPM-to-LPM converter<\/a> uses the US gallon by default, accurate to 13 decimal places.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1600\" height=\"1222\" src=\"\/blog\/wp-content\/uploads\/2026\/05\/step-01-converter-7.png\" alt=\"Full view of the xconvert GPM to LPM converter page with breadcrumbs, From and To unit selectors, and the conversion result\" class=\"wp-image-494\" srcset=\"\/blog\/wp-content\/uploads\/2026\/05\/step-01-converter-7.png 1600w, \/blog\/wp-content\/uploads\/2026\/05\/step-01-converter-7-300x229.png 300w, \/blog\/wp-content\/uploads\/2026\/05\/step-01-converter-7-1024x782.png 1024w, \/blog\/wp-content\/uploads\/2026\/05\/step-01-converter-7-768x587.png 768w, \/blog\/wp-content\/uploads\/2026\/05\/step-01-converter-7-1536x1173.png 1536w\" sizes=\"auto, (max-width: 1600px) 100vw, 1600px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"example\">Worked example: sizing a pool pump<\/h2>\n\n\n\n<p>Suppose you\u2019re shopping for a pool pump and the US-built model lists <strong>40 GPM<\/strong> at the rated head. You want to compare it to a European model rated at <strong>150 LPM<\/strong>. Which is bigger?<\/p>\n\n\n\n<p>Step 1 \u2014 Convert the US flow to LPM:<\/p>\n\n\n\n<p>Step 2 \u2014 Compare:<\/p>\n\n\n\n<p>The pumps are within 1% of each other. For most residential pool applications, that\u2019s effectively the same. If the difference came out to 10% or more, you\u2019d revisit pump curves and run a more careful analysis at your operating head, not just at the rated point.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"table\">Quick reference table<\/h2>\n\n\n\n<p>Common GPM values converted to LPM (US gallons, four decimal places). For the full table from 0 to 1,000,000 GPM, see the table on the <a href=\"https:\/\/www.xconvert.com\/unit-converter\/gallons-per-minute-to-litres-per-minute\">converter page<\/a>.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"table table-hover\"><thead><tr><th>GPM<\/th><th>LPM<\/th><th>Typical use<\/th><\/tr><\/thead><tbody><tr><td>0.5<\/td><td>1.89<\/td><td>Drip irrigation emitter (single zone)<\/td><\/tr><tr><td>1.5<\/td><td>5.68<\/td><td>Low-flow showerhead (US federal max 2.5 GPM)<\/td><\/tr><tr><td>2.5<\/td><td>9.46<\/td><td>Standard residential showerhead<\/td><\/tr><tr><td>5<\/td><td>18.93<\/td><td>Garden hose at typical pressure<\/td><\/tr><tr><td>10<\/td><td>37.85<\/td><td>Small utility pump<\/td><\/tr><tr><td>15<\/td><td>56.78<\/td><td>Submersible well pump (low end)<\/td><\/tr><tr><td>25<\/td><td>94.64<\/td><td>Pool circulation pump (small inground)<\/td><\/tr><tr><td>40<\/td><td>151.42<\/td><td>Pool pump (medium inground)<\/td><\/tr><tr><td>60<\/td><td>227.12<\/td><td>Whole-house water service line at peak<\/td><\/tr><tr><td>100<\/td><td>378.54<\/td><td>Light commercial booster pump<\/td><\/tr><tr><td>250<\/td><td>946.35<\/td><td>Industrial process pump<\/td><\/tr><tr><td>500<\/td><td>1,892.71<\/td><td>Mid-size irrigation main<\/td><\/tr><tr><td>1,000<\/td><td>3,785.41<\/td><td>Large agricultural irrigation, fire pump<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"common-rates\">Common pump and plumbing flow rates<\/h2>\n\n\n\n<p>A few benchmark numbers you\u2019ll meet repeatedly when reading specs:<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li><strong>US shower head federal maximum:<\/strong> 2.5 GPM = 9.46 LPM (since 1992 EPAct)<\/li><li><strong>WaterSense low-flow showerhead:<\/strong> 2.0 GPM = 7.57 LPM<\/li><li><strong>WaterSense bathroom (lavatory) faucet:<\/strong> 1.5 GPM = 5.68 LPM (federal max for <strong>kitchen<\/strong> faucets is 2.2 GPM; no WaterSense kitchen-faucet spec)<\/li><li><strong>Standard garden hose at 40 psi:<\/strong> ~5 GPM = ~19 LPM<\/li><li><strong>Typical residential well pump:<\/strong> 8\u201325 GPM = 30\u201395 LPM<\/li><li><strong>Pool pump (residential inground):<\/strong> 30\u201380 GPM = 113\u2013303 LPM<\/li><li><strong>Fire sprinkler head (residential):<\/strong> 10 GPM minimum = 38 LPM<\/li><li><strong>NFPA 13 light-hazard sprinkler design density:<\/strong> 0.10 GPM\/ft\u00b2 = 4.07 LPM\/m\u00b2 over 1500 ft\u00b2 (NFPA 13D residential is the lower 0.05 GPM\/ft\u00b2)<\/li><\/ul>\n\n\n\n<p>When a manufacturer publishes one number, that\u2019s usually the rated flow at the design head. Real flow varies with system head, age of the pump, and water temperature.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"faq\">Frequently Asked Questions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Why is GPM \u00d7 3.78541 and not exactly 3.79?<\/h3>\n\n\n\n<p>3.78541 is the precise definition of the US liquid gallon: exactly 231 cubic inches, which works out to 3.785411784 litres. Rounding to 3.79 introduces a 0.01% error \u2014 negligible at small flows, but at 10,000 GPM that\u2019s a 12.5 LPM discrepancy. xconvert\u2019s converter uses 13 decimal places to keep the error below detection.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Is \u201cgpm\u201d always the US gallon?<\/h3>\n\n\n\n<p>In US specifications, yes. In UK or older Commonwealth specifications, \u201cgpm\u201d can mean Imperial gallons per minute, and the conversion factor is 4.54609 instead of 3.78541. When in doubt, look at the country of origin of the spec sheet. If a UK manufacturer publishes flow in \u201cgallons,\u201d default to Imperial.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">How do I convert LPM back to GPM?<\/h3>\n\n\n\n<p>Divide by 3.78541, or equivalently multiply by 0.264172. So 100 LPM \u00f7 3.78541 \u2248 <strong>26.4 GPM<\/strong>. xconvert offers the <a href=\"https:\/\/www.xconvert.com\/unit-converter\/litres-per-minute-to-gallons-per-minute\">LPM-to-GPM reverse converter<\/a> directly.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">What about gallons per second or hour?<\/h3>\n\n\n\n<p>Same factors, just multiplied or divided by 60. For instance, 5 gallons per second = 5 \u00d7 60 = 300 GPM = 1135.6 LPM. xconvert has dedicated converters for <a href=\"https:\/\/www.xconvert.com\/unit-converter\/gallons-per-second-to-litres-per-minute\">GPS<\/a>, <a href=\"https:\/\/www.xconvert.com\/unit-converter\/gallons-per-hour-to-litres-per-minute\">GPH<\/a>, and other time bases.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Do I need to worry about water temperature?<\/h3>\n\n\n\n<p>For everyday plumbing and pump sizing \u2014 no. Water density changes by less than 4% from 0 \u00b0C to 100 \u00b0C, and flow rate is volume-based, not mass-based. The US gallon is defined as a fixed volume regardless of temperature. If you\u2019re working with cryogenic fluids or measuring mass flow, that\u2019s a different problem entirely.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">How accurate does the conversion need to be for plumbing?<\/h3>\n\n\n\n<p>For residential and most commercial plumbing, three significant figures is plenty. A 30 GPM pump rounded to 113.6 LPM (instead of 113.5623) is well within the noise of pump-curve uncertainty and aging. For laboratory or process-engineering work, use the full 3.78541 factor.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Try it now<\/h2>\n\n\n\n<p>Convert any GPM value to LPM (or back) with the <a href=\"https:\/\/www.xconvert.com\/unit-converter\/gallons-per-minute-to-litres-per-minute\">xconvert GPM-to-LPM converter<\/a> \u2014 full precision, no sign-up. For the reverse, use <a href=\"https:\/\/www.xconvert.com\/unit-converter\/litres-per-minute-to-gallons-per-minute\">LPM to GPM<\/a>. Need other flow-rate units? See <a href=\"https:\/\/www.xconvert.com\/unit-converter\/volumeFlowRate\">Volume Flow Rate<\/a> for the full catalog (m\u00b3\/h, L\/s, ft\u00b3\/min, and more).<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Convert gallons per minute (GPM) to liters per minute (LPM) with the exact formula, the US-vs-UK gallon distinction that trips up most calculators, and a quick-reference table for common pump and plumbing flow rates.<\/p>\n","protected":false},"author":3,"featured_media":493,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5,14],"tags":[],"class_list":["post-379","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-how-to-guides","category-tools"],"_links":{"self":[{"href":"\/blog\/wp-json\/wp\/v2\/posts\/379","targetHints":{"allow":["GET"]}}],"collection":[{"href":"\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"\/blog\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"\/blog\/wp-json\/wp\/v2\/comments?post=379"}],"version-history":[{"count":2,"href":"\/blog\/wp-json\/wp\/v2\/posts\/379\/revisions"}],"predecessor-version":[{"id":495,"href":"\/blog\/wp-json\/wp\/v2\/posts\/379\/revisions\/495"}],"wp:featuredmedia":[{"embeddable":true,"href":"\/blog\/wp-json\/wp\/v2\/media\/493"}],"wp:attachment":[{"href":"\/blog\/wp-json\/wp\/v2\/media?parent=379"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"\/blog\/wp-json\/wp\/v2\/categories?post=379"},{"taxonomy":"post_tag","embeddable":true,"href":"\/blog\/wp-json\/wp\/v2\/tags?post=379"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}