Pump flow units — GPM, LPM and m³/h
Same pump curve, three flow axes. Pick the wrong one and best-efficiency-point drifts by 20%.
Centrifugal pump curves come with the flow axis in whatever the manufacturer's home country prefers. Selecting a pump means matching duty flow — and unit — precisely, or you land off the BEP and destroy efficiency.
The exact factors
1 US gpm = 3.7854 L/min = 0.22712 m³/h = 0.06309 L/s > 1 UK gpm = 4.546 L/min = 0.27277 m³/h (20% larger than US gpm) > 1 m³/h = 4.403 US gpm = 3.666 UK gpm = 16.67 L/min
Where each is used
US gpm: North American water, HVAC, fire pumps. UK gpm: UK water utilities, occasional legacy specs. L/min and L/s: European water and HVAC. m³/h: process industry, chemical, EU pump vendors. bbl/day: oil production.
Worked example — HVAC chiller loop
A chiller specced 200 US gpm = 45.4 m³/h = 757 L/min. A European pump vendor's 45 m³/h pump is right on duty. A pump specced '200 gpm' from a UK vendor is 20% higher than intended — wildly oversized, throttling wastes 30% power.
Recap
US and UK gallons differ by 20%. Convert to m³/h or L/min once, compare.
Try the converters mentioned in this article
FAQ
Is US gpm the same as fluid-ounce-based gpm?+
US gpm uses 128 fl oz per gallon by the US gallon (231 in³). Do not use UK fl oz to derive it.
Which unit for oil-field pumps?+
bbl/day for production, gpm or L/min for surface pumps. Convert with 1 bbl = 42 US gal.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-07 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.