- The formula and conversion factor<\/a><\/li>
- Why L\/s shows up where it does<\/a><\/li>
- Quick reference table<\/a><\/li>
- Worked example: water-treatment plant capacity<\/a><\/li>
- Common engineering benchmarks<\/a><\/li>
- FAQ<\/a><\/li><\/ul>\n\n\n\n
The formula and conversion factor<\/h2>\n\n\n\n
The conversion is a single multiplication:<\/p>\n\n\n\n
For higher precision, use 15.8503231415 (the exact factor from US gallons being defined as 231 in\u00b3 = 3.78541178\u2026 L). xconvert\u2019s L\/s to GPM converter<\/a> carries 13 decimal places.<\/p>\n\n\n\n
![\"Full](\"\/blog\/wp-content\/uploads\/2026\/05\/step-01-converter-10.png\")
<\/figure>\n\n\n\nThe formula derivation is straightforward: 1 L\/s \u00d7 (60 s \/ 1 min) \u00d7 (1 gal \/ 3.78541 L) = 15.8503 gal\/min. Multiplying by 60 (seconds in a minute) and dividing by 3.78541 (litres in a US gallon) gives the factor.<\/p>\n\n\n\n
If you\u2019ve memorized other flow conversions, here\u2019s how L\/s relates:<\/p>\n\n\n\n
Why L\/s shows up where it does<\/h2>\n\n\n\n
The choice of unit is a tell about who designed the equipment:<\/p>\n\n\n\n
- Water-treatment plants<\/strong> publish capacity in L\/s (for small) or m\u00b3\/h (for large). 1 L\/s plant \u2248 a small village; 100 L\/s \u2248 a mid-size town.<\/li>
- Wastewater pumps<\/strong> are commonly rated in L\/s in EU and ANZ standards, GPM in the US.<\/li>
- Hydraulic systems<\/strong> (industrial machinery, presses) use L\/s for fluid power because the flows are small (1\u201320 L\/s) and L\/s gives readable numbers.<\/li>
- Drainage and stormwater design<\/strong> use L\/s for sub-watershed catchments, m\u00b3\/s for entire watersheds.<\/li>
- Process instrumentation<\/strong> (flowmeters with 4-20 mA outputs) is often spanned in L\/s because it\u2019s an SI-derived unit and matches PLC engineering culture.<\/li><\/ul>\n\n\n\n
When a US plant operator inherits a European-spec instrument, the L\/s readout is a constant friction. Either you re-span the instrument to GPM (if the protocol allows) or you train the operator to do the conversion mentally. The mental version: divide by 16 for a rough GPM, then add 1% (since the actual factor is 15.85, not 16).<\/p>\n\n\n\n
Quick reference table<\/h2>\n\n\n\n
L\/s<\/th> GPM<\/th> Typical context<\/th><\/tr><\/thead> 0.1<\/td> 1.59<\/td> Small dosing pump<\/td><\/tr> 0.5<\/td> 7.93<\/td> Hydraulic system fluid flow<\/td><\/tr> 1<\/td> 15.85<\/td> Domestic water main at peak<\/td><\/tr> 2<\/td> 31.70<\/td> Light commercial well pump<\/td><\/tr> 5<\/td> 79.25<\/td> Small water-treatment skid<\/td><\/tr> 10<\/td> 158.50<\/td> Industrial process feed<\/td><\/tr> 25<\/td> 396.26<\/td> Wastewater lift station (small)<\/td><\/tr> 50<\/td> 792.52<\/td> Mid-size water booster<\/td><\/tr> 100<\/td> 1,585.03<\/td> Municipal water-treatment basin<\/td><\/tr> 250<\/td> 3,962.58<\/td> Large industrial cooling water<\/td><\/tr> 500<\/td> 7,925.16<\/td> Major pump station<\/td><\/tr> 1,000<\/td> 15,850.32<\/td> Watershed-scale pump (large)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n Worked example: water-treatment plant capacity<\/h2>\n\n\n\n
A specification calls for a small water-treatment skid rated 8 L\/s at 5 bar discharge<\/strong>. The available US-built pump on hand is a Goulds 3656 SP<\/strong> at 130 GPM at 70 psi. Will it work?<\/p>\n\n\n\n
Step 1 \u2014 Convert flow:<\/strong><\/p>\n\n\n\n
The required is 126.8 GPM; the pump delivers 130 GPM. Within 3% \u2014 the system curve will shift the operating point slightly to compensate, and modulating valves can absorb the rest.<\/p>\n\n\n\n
Step 2 \u2014 Convert pressure to verify head margin:<\/strong><\/p>\n\n\n\n
The pump is 2.5 psi short on head. That\u2019s marginal. At the operating point, the pump curve might cross 70 psi at 126 GPM \u2014 barely meeting the requirement. Either confirm the operating-point head against the pump curve (not just rated head) or oversize the pump by going to a bigger frame.<\/p>\n\n\n\n
This is where unit conversion isn\u2019t just bookkeeping \u2014 it lets you make engineering judgements with confidence. Without converting, \u201c8 L\/s at 5 bar\u201d and \u201c130 GPM at 70 psi\u201d feel completely different. Once converted, the comparison is direct.<\/p>\n\n\n\n
Common engineering benchmarks<\/h2>\n\n\n\n
A few L\/s numbers worth knowing:<\/p>\n\n\n\n
- Small water service (residential):<\/strong> 0.5\u20131.0 L\/s = 8\u201316 GPM<\/li>
- Medium commercial water service:<\/strong> 5\u201310 L\/s = 80\u2013160 GPM<\/li>
- Building chilled-water distribution:<\/strong> ~0.043 L\/s per kW of cooling load (= 2.4 GPM\/ton, ASHRAE rule of thumb)<\/li>
- Storm-sewer design (urban catchment):<\/strong> 5\u201350 L\/s per hectare during 10-year storm<\/li>
- Wastewater lift-station typical:<\/strong> 10\u201350 L\/s = 160\u2013800 GPM<\/li>
- Water-treatment plant typical:<\/strong> 100\u20131,000 L\/s = 1,600\u201316,000 GPM<\/li>
- Hydraulic press circuit:<\/strong> 0.5\u20135 L\/s per actuator<\/li>
- Fire pump (EU spec):<\/strong> 30\u201360 L\/s = 475\u2013950 GPM<\/li>
- River flow (small creek):<\/strong> 1\u201310 L\/s baseflow<\/li>
- Sewage treatment per capita:<\/strong> 200\u2013400 L\/day per person \u2248 0.0023\u20130.0046 L\/s per person<\/li><\/ul>\n\n\n\n
Frequently Asked Questions<\/h2>\n\n\n\n
Why isn\u2019t L\/s the SI unit for flow?<\/h3>\n\n\n\n
The SI unit for volumetric flow is m\u00b3\/s. L\/s is a derived unit (1 L = 0.001 m\u00b3, so 1 L\/s = 0.001 m\u00b3\/s) but allowed under the SI brochure. It survives because the numbers are friendlier in everyday engineering: a 50 L\/s plant is more legible than 0.05 m\u00b3\/s. For very large flows (rivers, storm sewers) m\u00b3\/s starts to win.<\/p>\n\n\n\n
What\u2019s the difference between L\/s and L\/min?<\/h3>\n\n\n\n
Just a factor of 60. 1 L\/s = 60 L\/min = 60 LPM. The unit choice tracks the size of the system: LPM for residential and small commercial (where flows are 0.1\u201310 L\/s), L\/s for industrial and treatment (where flows are 1\u20131000 L\/s). For very small flows (drip irrigation, single faucets), GPH or LPM gives more readable numbers.<\/p>\n\n\n\n
Is there an Imperial version of L\/s?<\/h3>\n\n\n\n
The litre is metric, so L\/s is metric only. The Imperial-system equivalents are GPM (US gallon) or imp gpm (Imperial gallon). 1 L\/s = 15.85 US GPM = 13.20 imp GPM. UK water-industry specifications use either L\/s or m\u00b3\/h depending on the era of the document.<\/p>\n\n\n\n
How do I convert L\/s to mass flow rate?<\/h3>\n\n\n\n
Multiply by fluid density. For water at 20 \u00b0C: 1 L\/s \u00d7 998.2 kg\/m\u00b3 = 0.998 kg\/s \u2248 1 kg\/s<\/strong>. The \u201c1 L\/s \u2248 1 kg\/s\u201d approximation is good to within 0.5% across the typical operating range of clean water systems. For other fluids (oil, ammonia, brine), use the actual density from the fluid datasheet.<\/p>\n\n\n\n
Why does my flow meter read in L\/s but the controller works in GPM?<\/h3>\n\n\n\n
Industrial flow meters often output 4\u201320 mA spanned in L\/s (an EU-style configuration), but US-built PLCs and SCADA systems typically scale display values in GPM. The fix is in the PLC scaling: change the analog input scale factor to convert the 4\u201320 mA range to GPM before storing\/displaying. Or change the meter\u2019s span to GPM if the protocol allows it. Don\u2019t do the conversion in the operator\u2019s head \u2014 that\u2019s where errors compound.<\/p>\n\n\n\n
What\u2019s the relationship between L\/s and pipe size?<\/h3>\n\n\n\n
For full-pipe flow at typical velocities (1\u20133 m\/s for water mains), the rough relationship is:<\/p>\n\n\n\n
- DN50 (2") pipe at 2 m\/s: ~4 L\/s<\/li>
- DN100 (4") at 2 m\/s: ~16 L\/s<\/li>
- DN150 (6") at 2 m\/s: ~35 L\/s<\/li>
- DN200 (8") at 2 m\/s: ~63 L\/s<\/li>
- DN300 (12") at 2 m\/s: ~141 L\/s<\/li><\/ul>\n\n\n\n
These are rough \u2014 actual flow depends on pipe internal diameter and velocity, and you should use the Hazen-Williams or Darcy-Weisbach equations for friction loss in design. Use them for sanity-checks: if a spec says \u201cDN100 at 200 L\/s,\u201d somebody made a mistake (that would require 12+ m\/s velocity, which is far above the usual design ceiling).<\/p>\n\n\n\n
Try it now<\/h2>\n\n\n\n
Convert any L\/s value with the xconvert L\/s to GPM converter<\/a> \u2014 full precision, instant. For other flow-rate pairs (LPM, m\u00b3\/h, CFM, m\u00b3\/s), see the Volume Flow Rate<\/a> catalog. For the broader picture of which industries use which units, our Flow Rate Conversion for HVAC and Plumbing<\/a> overview is the place to start.<\/p>\n","protected":false},"excerpt":{"rendered":"
Convert L\/s to GPM with the exact \u00d715.85 multiplier, plus a quick-reference table for 0.1 to 100 L\/s and real-world examples from process engineering, water treatment, and pump sizing.<\/p>\n","protected":false},"author":3,"featured_media":505,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5,14],"tags":[],"class_list":["post-394","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\/394","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=394"}],"version-history":[{"count":1,"href":"\/blog\/wp-json\/wp\/v2\/posts\/394\/revisions"}],"predecessor-version":[{"id":507,"href":"\/blog\/wp-json\/wp\/v2\/posts\/394\/revisions\/507"}],"wp:featuredmedia":[{"embeddable":true,"href":"\/blog\/wp-json\/wp\/v2\/media\/505"}],"wp:attachment":[{"href":"\/blog\/wp-json\/wp\/v2\/media?parent=394"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"\/blog\/wp-json\/wp\/v2\/categories?post=394"},{"taxonomy":"post_tag","embeddable":true,"href":"\/blog\/wp-json\/wp\/v2\/tags?post=394"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- Medium commercial water service:<\/strong> 5\u201310 L\/s = 80\u2013160 GPM<\/li>
- Wastewater pumps<\/strong> are commonly rated in L\/s in EU and ANZ standards, GPM in the US.<\/li>
- Why L\/s shows up where it does<\/a><\/li>