Flow Rate Converter
Convert volumetric flow between m³/h, L/s, L/min, US and UK gal/min, cfm, cfs, MGD and barrels/day, plus mass flow and pipe velocity from your inputs.
One flow figure in every unit the pump curve, the datasheet and the spec sheet use, from exact gallon and cubic-foot definitions rather than rounded factors.
Example: 100 US gal/min = 6.309 L/s = 22.71 m³/h = 13.37 cfm = 83.27 UK gal/min = 0.144 MGD; in a 3 in bore that is 1.38 m/s.
Exact definitions,
not rounded factors.
Which gallon is which, where the factors come from, and what the optional mass and velocity figures assume.
The two gallons and the cubic foot
A US gallon is exactly 3.785 411 784 litres (231 cubic inches); a UK or imperial gallon is exactly 4.546 09 litres — about 20 % larger. Pump curves from US makers, well and irrigation figures and most “gpm” on the web are US; older British and some Commonwealth documents are imperial. Both are listed so the ambiguity is visible. The cubic foot is 28.316 846 592 litres exactly (from the inch of 25.4 mm), the petroleum barrel is 42 US gallons, and MGD is a million US gallons per day.
How the conversion is done
The entered value is converted to cubic metres per second with the exact factor for its unit and then to every other unit; no chained rounded factors. The values shown are rounded for display only. Days are 86,400 seconds; the converter does not know about working days or hours of operation — apply those yourself.
Mass flow and velocity
Enter a density and the same flow is also shown as kg/s, kg/h, t/h and lb/h (mass = volume × density; density depends on the fluid and its temperature, so none is assumed). Enter a pipe bore and the average velocity in that bore is shown (v = Q ÷ πD²/4) — use the inside diameter, not the nominal size. Gas flows quoted at standard conditions (SCFM, Nm³/h) are mass-like quantities that depend on the reference pressure and temperature; this page converts volumes only and does not correct them.
Privacy
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SOURCES
- NIST Special Publication 811 (2008), Guide for the Use of the SI, Appendix B — gallon (US) 3.785 411 784 L, cubic foot 0.028 316 846 592 m³, barrel (petroleum) 42 US gal
- UK Weights and Measures Act 1985, Schedule 1 — gallon = 4.546 09 cubic decimetres
Last reviewed 19 September 2026. How results are checked: How we verify.