Units and SI factors
All units are referenced to the SI base m³/s (Cubic metre per second).
| Unit | Name | Factor to SI | 1 unit = ? SI |
|---|
Volumetric flow rate in engineering practice
Volumetric flow rate is the volume of fluid passing a point per unit time, with SI unit cubic metres per second (m³/s). Because that unit is huge for most systems, engineers work in cubic metres per hour (m³/h), litres per minute (L/min) and litres per second (L/s). In the US the customary units are US gallons per minute (US gpm) and, for air, cubic feet per minute (CFM).
Where each unit shows up
- m³/h — water-treatment plants, large pumps and chilled-water circuits.
- L/min — fuel flow, small pumps and medical oxygen delivery.
- L/s — fire-suppression systems and laboratory dosing.
- US gpm — US plumbing, irrigation and pump specifications.
- CFM — air compressors, HVAC fans and dust collection.
Conversion gotchas
Do not confuse the US gallon (3.7854 L) with the imperial gallon (4.546 L) — an imperial gpm is about 20% larger. For gases, the physical volume changes with temperature and pressure, so CFM figures are often quoted at “standard” conditions; check which reference applies. Useful anchors: 1 m³/h ≈ 0.2778 L/s and 1 L/min ≈ 0.2642 US gpm.