Skip to content
ToolBoxGeniehome

Flow Rate Converter

Converters · Added

Pump curves, compressor ratings, irrigation specs and plumbing codes each quote flow in their own units, and the conversions between them are exact but tedious. Every factor here is a volume divided by a time — both defined exactly — so the answers carry no approximation beyond the arithmetic. The two traps worth knowing about are gallons and mass, and both are covered below.

Result

1 L/min in us gallon per minute

0.264172052 GPM (US)

1 L/min = 0.264172052 GPM (US)

The same value in every unit

Cubic metre per second (m³/s)
0.0000166666667
Cubic metre per minute (m³/min)
0.001
Cubic metre per hour (m³/h)
0.06
Litre per second (L/s)
0.0166666667
Litre per minute (L/min)
1
Litre per hour (L/h)
60
Millilitre per second (mL/s)
16.6666667
Millilitre per minute (mL/min)
1,000
US gallon per minute (GPM (US))
0.264172052
US gallon per hour (GPH (US))
15.8503231
US gallon per day (GPD (US))
380.407755
Imperial gallon per minute (GPM (UK))
0.219969248
Imperial gallon per hour (GPH (UK))
13.1981549
Cubic foot per second (ft³/s (cusec))
0.000588577779
Cubic foot per minute (CFM)
0.0353146667
Cubic foot per hour (ft³/h)
2.11888
Oil barrel per day (bbl/d)
9.05732751
Oil barrel per hour (bbl/h)
0.377388646

US and imperial gallons per minute differ by about 17%, so a GPM figure means nothing until you know which gallon it counts — both are listed separately here. Note also that this converts volume per unit time; mass flow in kg/s needs the fluid's density, and for a gas that means a stated temperature and pressure too.

How to use the flow rate converter

  1. 1Enter the flow rate you have.
  2. 2Pick the unit it is quoted in. US and imperial gallons are listed separately on purpose — they are not the same size.
  3. 3Pick the unit you want it in.
  4. 4The converted value appears immediately, alongside the same rate in the other common units.
  5. 5Swap the two selections to reverse the conversion.

Examples

A domestic shower

Input
9 litres per minute
Result
About 2.38 US GPM, or 0.54 cubic metres per hour

Low-flow showerheads are typically specified at or below 9 L/min in metric markets and 2.5 GPM in the US — which are close but not identical thresholds.

A pump specified in imperial gallons

Input
10 imperial GPM
Result
About 12.01 US GPM, or 45.46 litres per minute

A 20% difference for the same number on the label. This is the conversion that quietly undersizes pumps bought across markets.

An air compressor

Input
200 CFM
Result
About 5.66 cubic metres per minute, or 94.4 litres per second

Volumetric only. What mass of air that represents depends on the pressure and temperature it was measured at, which is why compressor ratings state a reference condition.

About the flow rate converter

Where each unit is actually used

Flow rate units are strongly regional and strongly by-industry, which is why conversion comes up so often. Plumbing and domestic appliances in metric markets use litres per minute; the same products in the US are rated in gallons per minute. Pumps and HVAC water systems tend towards cubic metres per hour, because it lines up neatly with tank volumes and hourly duty cycles. Compressed air is cubic feet per minute nearly everywhere, including in countries that use metric for everything else.

Larger scales change units again. Municipal water is often megalitres per day, river and canal discharge in South Asia is cusecs, and oil is barrels per day worldwide. Laboratory work goes the other way into millilitres per minute, and medical infusion into millilitres per hour.

None of these are conversions with any subtlety to them — a volume factor over a time factor, both exact by definition — but there are enough of them, and the numbers are awkward enough, that doing it in your head reliably is not realistic.

Volume is not mass, and it matters most for gases

Everything on this page is volumetric flow: how much space per unit time. For a liquid at ordinary temperatures that is nearly interchangeable with mass, because liquids barely compress — water is close enough to a kilogram per litre that plumbing calculations rarely distinguish the two.

Gases are different in kind. Air at ten bar occupies roughly a tenth of the volume it does at atmospheric pressure, so 200 CFM measured at the compressor outlet and 200 CFM measured at the inlet describe very different quantities of air. This is exactly why compressed-air equipment is specified in SCFM or in normal cubic metres per hour, both of which state the temperature and pressure the volume was reduced to. Comparing a plain CFM figure with an SCFM one is comparing two different measurements that happen to share a unit.

The practical rule is to check what any gas flow figure was referenced to before converting it, and to treat a mass flow requirement as needing a density you have to supply. For liquids, the conversion here is the whole job; for gases, it is the first step of one.

Frequently asked questions

Is GPM American or British?
Both, and that is the problem. A US gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres, so the same GPM figure describes flows about 20% apart depending on which side of the Atlantic the specification came from. This converter lists them as separate units and never abbreviates either to a bare GPM, because a pump chosen on the wrong gallon is a real and expensive mistake.
How do I convert this to kilograms per second?
You cannot, without knowing the fluid. Volumetric flow and mass flow are different quantities, related by density — mass flow equals volume flow times density. For water near room temperature that is close to 1 kg per litre, so 60 L/min is roughly 1 kg/s. For a gas, density depends on both temperature and pressure, so the same cubic metres per hour can be several times more or less mass depending on conditions. Any converter that offers you kg/s from L/min without asking what is flowing has assumed something on your behalf.
What is a cusec?
One cubic foot per second, the traditional unit for river and canal flow in India, Pakistan and parts of the US. It is about 28.32 litres per second, or 1,699 litres per minute. Irrigation discharge and dam release figures are still quoted in cusecs in official bulletins, which is usually why someone needs to convert one.
Is CFM at standard conditions?
Not here. This converter changes units, and a plain cubic foot per minute is a volume of air per minute at whatever conditions it was measured. Compressor specifications often use SCFM instead, which is CFM corrected to a stated reference temperature and pressure so that two machines can be compared. Converting between CFM and SCFM needs those reference conditions and is a different calculation from a unit conversion.
Why is a barrel per day here?
Because production and pipeline figures in the oil industry are quoted in barrels per day almost universally, and converting them to anything else by hand is unpleasant. The oil barrel is exactly 42 US gallons, or about 158.99 litres, and one barrel per day works out to roughly 0.11 litres per minute.

Related tools