About the Flow Rate Converter
This flow rate converter translates a volumetric flow between the units used by pumps, plumbing, HVAC and process equipment: liters per minute and per second, cubic meters per hour, US and UK gallons per minute, gallons per hour, cubic feet per minute (CFM), cubic feet per second and oil barrels per day. Enter one value, choose its unit and every equivalent appears at once.
Plumbers and irrigation installers use it to compare a US pump rated in GPM with a European one rated in L/min or m³/h; HVAC technicians convert CFM airflow to metric; and engineers check pipe, well and process flows. An optional tank volume shows how long the flow would take to fill it.
Conversions use exact unit definitions — the US gallon is 3.785411784 L, the UK gallon 4.54609 L and a cubic foot 28.316846592 L — so results are precise. Real pump output depends on head, pressure and pipe losses, so treat rated flows as maximums.
With the default inputs, the liters per minute is 37.854 L/min. Change any value above to recalculate instantly.
How to use the flow rate converter
- 1Enter the flow rate value.
- 2Select the unit it is given in (GPM, L/min, CFM, m³/h…).
- 3Read the equivalent in every other unit.
- 4Optionally enter a tank or pool volume in liters to estimate fill time.
Formula and method
Every unit is converted through liters per second. One US gallon is exactly 3.785411784 L, so 1 GPM = 3.785411784 L/min = 0.0630902 L/s. One cubic foot is 28.316846592 L, so 1 CFM = 28.3168 L/min. One cubic meter per hour is 1,000 L ÷ 60 = 16.667 L/min, and an oil barrel is 42 US gallons (158.987 L).
Fill time is simply volume ÷ flow: a 1,000 L tank at 37.85 L/min fills in about 26.4 minutes, ignoring any drop in flow as pressure changes.
- Q
- Volumetric flow rate (volume per unit time)
- V
- Volume to fill
- t
- Fill time = V ÷ Q
Worked examples
A 10 GPM pump in metric
10 × 3.785411784 = 37.85 L/min, or 2.27 m³/h. At that rate a 1,000-liter tank fills in 1,000 ÷ 37.85 = 26.4 minutes.
Bathroom fan at 50 m³/h
50 m³/h is 50,000 L ÷ 60 = 833.3 L/min, and dividing by 28.3168 L per cubic foot gives 29.4 CFM — the airflow rating a US fan would show.
1,000 CFM air handler
1,000 × 28.3168 = 28,317 L/min, or 471.9 L/s. Multiplying L/s by 3.6 gives 1,699 m³/h.
Frequently asked questions
How do I convert GPM to liters per minute?+
Multiply US gallons per minute by 3.785. For example, 5 GPM × 3.785411784 = 18.93 L/min. For UK gallons multiply by 4.546 instead.
How do I convert CFM to m³/h?+
Multiply CFM by 1.699. One cubic foot per minute is 28.3168 liters per minute, which is 1.699 cubic meters per hour.
How many GPM is 1 liter per second?+
One liter per second is 60 liters per minute, which equals 15.85 US gallons per minute or 13.20 UK gallons per minute.
What is the difference between US and UK GPM?+
A UK (imperial) gallon is 4.54609 L while a US gallon is 3.785411784 L, so 1 UK GPM equals about 1.2 US GPM. Always check which gallon a spec sheet uses.
Is CFM used for water flow?+
CFM is mostly used for air and gas flow in HVAC and compressors. Water flow is usually quoted in GPM, L/min or m³/h, but the volume conversion is identical.