# Flow rate converter

> Convert L/min to gpm, gpm to L/min, cfm to m³/h and m³/h to L/s for pumps, plumbing and ventilation, with the exact US gallon and cubic foot.

Interactive version: https://www.calcopenly.com/conversion/flow-rate-converter
Subject: Unit converters

Flow rate is volume per time, and each unit here is a fixed number of cubic metres per second. The US gallon (3.785411784 L) and the cubic foot (28.316846592 L) are exact, so litres per minute, gallons per minute and cubic feet per minute convert with no rounding in the factors.

The default converts 10 L/min to 2.64 US gpm, close to the 2.5 gpm (9.46 L/min) of a standard US showerhead. Plumbers and pump buyers use L/min and gpm, fan and compressor ratings use cfm or m³/h, and river flows are reported in m³/s (cumecs).

The gallon here is the US gallon. An imperial gallon per minute is 4.54609 L/min, 20% more, so check which gallon a specification uses before converting it.

## Inputs

- **Value**: A number in the “from” unit, or with its own unit
- **From** (options: cubic metre per second (m³/s), cubic metre per hour (m³/h), litre per second (L/s), litre per minute (L/min), litre per hour (L/h), US gallon per minute (gal/min), cubic foot per minute (ft³/min))
- **To** (options: cubic metre per second (m³/s), cubic metre per hour (m³/h), litre per second (L/s), litre per minute (L/min), litre per hour (L/h), US gallon per minute (gal/min), cubic foot per minute (ft³/min))

## Results

- Converted value — main result
- Conversion
- Conversion factor
- Exactness

## Formula

$$
\begin{gathered} x_{\text{to}} = x_{\text{from}} \times \dfrac{f_{\text{from}}}{f_{\text{to}}} \\ f = \text{one unit expressed in } \text{m³/s} \end{gathered}
$$

## Worked examples

### 10 L/min in US gal/min

- Value: 10 L/min
- From: litre per minute (L/min)
- To: US gallon per minute (gal/min)
- **Converted value: 2.6417205236 gal/min**
- Checked against: 10 L ÷ 3.785411784 L = 1250000000/473176473 (Python 3.8 fractions from the legal definitions)

### 1 m³/s in L/s

- Value: 1 m³/s
- From: cubic metre per second (m³/s)
- To: litre per second (L/s)
- **Converted value: 1,000 L/s**
- Checked against: 1 m³ = 1000 L

### 1 cfm in L/min

- Value: 1 ft³/min
- From: cubic foot per minute (ft³/min)
- To: litre per minute (L/min)
- **Converted value: 28.316846592 L/min**
- Checked against: 1 ft³ = 0.3048³ m³ = 28.316846592 L (NIST HB 44 App. C)

### 1 m³/h in L/s

- Value: 1 m³/h
- From: cubic metre per hour (m³/h)
- To: litre per second (L/s)
- **Converted value: 0.2777777778 L/s**
- **Exactness: Exact definitions, repeating decimal**
- Checked against: 1000 L / 3600 s = 5/18

## Questions

### How do I convert L/min to gpm?

Divide by 3.785411784, or multiply by 0.264172. 10 L/min is 2.64 US gpm and 20 L/min is 5.28 gpm. To go from US gpm to L/min, multiply by 3.785, so a 2.5 gpm showerhead runs at 9.46 L/min.

### How do I convert cfm to m³/h?

Multiply by 1.69901. A cubic foot is 0.028316846592 m³ and an hour is 60 minutes, so 1 cfm = 1.69901079552 m³/h exactly. A 100 cfm bathroom fan moves 169.9 m³/h, or 47.2 L/s. To go from m³/h to cfm, multiply by 0.588578.

### What is a normal shower flow rate?

The US EPA puts standard showerheads at 2.5 gallons per minute, 9.46 L/min, and requires WaterSense-labelled ones to use no more than 2.0 gpm, 7.57 L/min. A 10-minute shower at 2.5 gpm uses 25 gallons, or 94.6 litres. Timing how long your shower takes to fill a 1-litre jug gives your own figure: 6 seconds means 10 L/min.

### How do I convert m³/h to L/s?

Divide by 3.6. A cubic metre is 1,000 litres and an hour 3,600 seconds, so 1 m³/h = 1,000/3,600 = 0.2778 L/s, a repeating decimal. A pump rated at 36 m³/h delivers exactly 10 L/s, or 600 L/min.

### Is gpm in US or imperial gallons?

In this converter, US gallons: 1 gpm = 3.785411784 L/min. Imperial gallons per minute are 4.54609 L/min, 20% larger, and appear on equipment specified in imperial units. To convert an imperial figure, multiply it by 1.20095 to get US gpm before entering it.

### How accurate is the flow rate converter?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 4 worked examples whose answers come from independent sources; for example, “10 L/min in US gal/min” is checked against 10 L ÷ 3.785411784 L = 1250000000/473176473 (Python 3.8 fractions from the legal definitions).

### Where does the method come from?

NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors; NIST Handbook 44, Appendix C — General tables of units of measurement.

## Sources

- [NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44, Appendix C — General tables of units of measurement](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)