Flow Rate Converter
Convert water and air flow between L/s, GPM, and cubic feet units.
What it does
Flow rate tells how much fluid passes per unit time. Pumps use gallons per minute, showers use liters per minute, and rivers use cubic feet per second. Converting between those units needs exact volume factors, not rounded guesses.
The tool above converts among L/s, L/min, m3/h, mL/s, US gal/min, ft3/s, and ft3/min. The defaults convert 10 L/min to US gal/min, so the page opens showing 2.6417 gal/min. Pick new units to update the result and the full list.
The math rests on two exact definitions. One inch is exactly 2.54 cm, so one US gallon, defined as 231 cubic inches, is exactly 3.785411784 liters. One foot is exactly 0.3048 m, so one cubic foot is exactly 28.316846592 liters. All flow factors derive from those two.
Use metric for lab and irrigation math, US units for American pumps and plumbing labels, and cubic feet for open channel flow. Keep the fluid in mind too: these are volume rates, so mass rates need density as a second step.
This page shows the factors, one full hand checked example at 10 L/min, a reference table, and practice checks that run through the tool.
How to use
- Type the flow number, for example 10.
- Pick the starting unit in From unit, for example Liters per minute.
- Pick the target unit in To unit, for example US gallons per minute.
- Read the main result with four decimals and unit name.
- Scan the note line for the same flow in all seven units.
- Recheck pump labels: US gallons differ from imperial gallons.
Formula
- L/s
- Base unit. 1 L/s = 60 L/min = 3.6 m3/h.
- gal/min
- US gallon per minute. 1 gal/min = 3.785411784 L/min.
- ft3/s
- Cubic foot per second. 1 ft3/s = 28.316846592 L/s.
Factors use exact definitions: 1 in = 2.54 cm and 1 ft = 0.3048 m. US gallons are used throughout. For imperial gallons, multiply US gal/min by 0.8327 first.
Worked example
Example: 10 L/min to US gal/min
A small pump moves 10 liters per minute. Convert to US gallons per minute.
- Write the inputs: 10, from L/min, to gal/min.
- Recall 1 US gallon = 3.785411784 liters, so 1 L/min = 1 / 3.785411784 gal/min.
- Divide: 10 / 3.785411784 = 2.6417205.
- Round to four decimals: 2.6417 gal/min.
- Cross check: 2.6417 x 3.785411784 = 10.00 L/min.
- Read the note line for siblings: 0.1667 L/s and 0.6 m3/h.
Reference table
| Unit | L/s per unit | Note |
|---|---|---|
| L/s | 1 | Base unit |
| L/min | 0.0166667 | Divide by 60 |
| m3/h | 0.2777778 | 1000 L per 3600 s |
| mL/s | 0.001 | 1000 mL per L |
| US gal/min | 0.0630902 | 3.785411784 L per gal |
| ft3/s | 28.3168466 | Exact from 0.3048 m foot |
| ft3/min | 0.4719474 | ft3/s divided by 60 |
Limits
- Volume rates only. Mass flow needs density as well.
- US gallons throughout. Imperial gallons need a separate 1.20095 factor.
- Does not model pressure loss, viscosity, or pump curves.
- Four decimals suit field work. Lab dosing may need more digits.
Common mistakes
- Using imperial gallons (4.546 L) where the tool uses US gallons (3.785 L).
- Mixing per second with per minute without the factor of 60.
- Reading m3/h as m3/s, which is off by 3600 times.
- Typing commas as thousand separators in the value box.
- Applying liquid factors to air without correcting for compressibility.
Try it yourself
Quick checks. Answers sit tucked under each question.
100 L/min in gal/min?
100 / 3.785411784 = 26.4172 gal/min.
5 gal/min in L/min?
5 x 3.785411784 = 18.9271 L/min.
Questions
How many L/min in 1 GPM?
3.785411784 L/min for US gallons.
How many GPM in 10 L/min?
2.6417 gal/min.
What is 1 CFS in L/s?
28.3168466 L/s.
US or imperial gallon?
This tool uses US gallons. Multiply US gal/min by 0.8327 for imperial gal/min.
Does temperature matter?
Not for volume rate. It matters when you convert to mass rate.
Why four decimals?
Enough for pumps and irrigation without hiding small errors.