Flow Rate Converter
Flow rate measures the volume of fluid (liquid or gas) passing through a point per unit time, essential for water systems, HVAC design, hydraulic engineering, and hydrology. The SI unit is cubic metres per second (m³/s), but practical applications use a variety of units depending on scale and region. Litres per minute (L/min) is standard for household and industrial water systems, while US gallons per minute (GPM) is common in the United States. Cubic feet per minute (CFM) is standard for air flow in HVAC systems. Hydrology and river engineering use cubic feet per second (CFS) and cubic metres per second (m³/s). Small flows use litres per second (L/s) or millilitres per second (mL/s). Converting between flow rate units is essential when specifying pumps, designing irrigation systems, selecting HVAC equipment, or comparing water treatment systems. A typical household faucet flows at 6 litres per minute, equivalent to about 1.6 GPM. This calculator displays eleven flow rate units: from millilitres per second to cubic feet per minute, with NIST-defined precision for instant conversion.
NIST conversion factors
All conversions below use standard NIST-defined factors, with all units expressed relative to the litre per second.
| Unit | Symbol | Litres per Second |
|---|---|---|
| Millilitre per second | mL/s | 0.001 |
| Litre per second | L/s | 1 |
| Litre per minute | L/min | 0.016667 |
| Litre per hour | L/h | 0.000277778 |
| Cubic metre per second | m³/s | 1,000 |
| Cubic metre per minute | m³/min | 16.667 |
| Cubic metre per hour | m³/h | 0.27778 |
| US gallon per minute | GPM | 0.063090 |
| US gallon per hour | GPH | 0.001052 |
| Cubic foot per second | CFS | 28.3168 |
| Cubic foot per minute | CFM | 0.47195 |
Flow rate converter: frequently asked questions
What is flow rate?
Flow rate measures the volume of fluid moving past a point per unit time. The SI unit is cubic metres per second (m³/s), but litres per minute and US gallons per minute are common in practical applications.
What is GPM?
GPM stands for gallons per minute, commonly used in the United States for water systems, irrigation, and hydraulic systems. One GPM equals about 0.063 litres per second or 3.785 litres per minute.
What is CFS?
CFS stands for cubic feet per second, used in hydrology and water engineering for measuring river and stream flow. One cubic foot per second equals about 28.3 litres per second.
How precise are these conversions?
These use NIST-defined conversion factors based on exact unit relationships. All conversions are mathematically precise to two decimal places.
Why do I need to convert flow rates?
Different countries and industries use different flow rate units. Water systems use L/min or GPM. Hydrology uses m³/s or CFS. HVAC systems use CFM. Converting ensures clarity when comparing specifications.
Official sources
- NIST Handbook 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices.
- NIST Special Publication 330: The International System of Units.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.