Flow Rate Converter (m³/h, L/min, L/s, CFM)

Understanding the flow rate converter — concept and principle

Volumetric flow rate is the volume of fluid that passes a point per unit of time. This converter switches between cubic metres per hour (m³/h), litres per minute and per second, cubic metres per second and per minute, and cubic feet per minute (CFM). It is used to compare fan and ventilation ratings, size pumps and compressors, and read equipment specifications written in metric or US units.

A cubic foot is 28.3 L, so 100 CFM = 2,831.7 L/min = 169.9 m³/h.

How it is calculated

Every unit is first converted to a common base, then to the target unit: result = value × (size of source unit) ÷ (size of target unit). In m³/h the unit sizes are:

1 L/min = 0.06 m³/h (60 min × 0.001 m³)
1 L/s = 3.6 m³/h
1 m³/min = 60 m³/h; 1 m³/s = 3,600 m³/h
1 CFM = 1.699010796 m³/h

The CFM factor comes from the exact definition of the foot: 1 ft = 0.3048 m, so 1 ft³ = 0.3048³ = 0.028316846592 m³, and 60 minutes per hour gives 1.699010796 m³/h.

The principle

A flow rate is a volume divided by a time, so converting it means converting the volume part and the time part separately and multiplying the two factors. Because every factor is a fixed ratio, the conversion is exact and linear: doubling the value doubles the result. No property of the fluid enters the calculation, which is why the same factors apply to air, water or oil, as long as you are talking about volume rather than mass.

Worked example

Inputs: 100 CFM, convert to m³/h.
Volume: 1 ft³ = 0.028316846592 m³, so 100 ft³ = 2.8316846592 m³ per minute.
Time: multiply by 60 minutes per hour: 2.8316846592 × 60 = 169.9010796 m³/h.
The same flow in other units: 2,831.684659 L/min, 47.19474432 L/s, 0.0471947443 m³/s and 2.831684659 m³/min.

How to read the result

For quick estimates, 1 CFM is about 1.7 m³/h, and 1 m³/h is about 0.59 CFM. A bathroom exhaust fan is often rated in the tens of CFM, while room air purifiers and kitchen hoods are commonly listed in hundreds of m³/h. Compare products only at the same test conditions: fan airflow drops as static pressure rises, so a free-air rating is higher than the flow through real ductwork.

Common mistakes

Treating standard CFM (SCFM, referenced to standard temperature and pressure) as the same as actual CFM; for compressed air they can differ greatly.
Confusing m³/h with m³/min, a factor of 60.
Using a volumetric conversion for mass flow (kg/h), which needs the fluid density.

Keep in mind: The conversion is exact, but the numbers you convert are often measured under specific test conditions. For ventilation, pump and compressor sizing, check the manufacturer's curves and local building or ventilation codes with a qualified professional.

Frequently asked questions

How many m³/h is 1 CFM?

1 CFM = 1.699010796 m³/h, roughly 1.7 m³/h.

How do I convert L/min to m³/h?

Multiply by 0.06. For example, 50 L/min = 3 m³/h.

How do I convert air changes per hour to a flow rate?

Multiply the room volume in m³ by the air changes per hour to get m³/h. A 30 m³ room at 4 changes per hour needs 120 m³/h.

Sources: NIST Special Publication 811 (2008), Guide for the Use of the International System of Units, Appendix B · BIPM, The International System of Units (SI Brochure), 9th edition

Checked 8 Nov 2026. Factors from the SI Brochure (BIPM, 9th ed.) and NIST Special Publication 811 (2008), Appendix B.