How do I convert CFM to m³/h (and back)?

One cubic foot per minute (CFM) equals 1.699 cubic metres per hour (m³/h). To convert: m³/h = CFM × 1.699, and CFM = m³/h ÷ 1.699. For SI purists, 1 CFM ≈ 0.0004719 m³/s. Getting units wrong between a European system model and a US datasheet is one of the most common first-pass selection errors.

Quick conversion table

Keep this table near your calculator — the factors are exact for volume flow. Note that pressure units do not convert by the same numbers: 1 inH₂O = 249.1 Pa and 1 mmH₂O = 9.807 Pa.

Why units alone are not the whole story

Heat transfer depends on mass flow (kg/s), not volume flow. If you convert units but ignore density, a fan tested at 20°C sea level will look equivalent to one spec'd at 60°C — a mismatch of roughly 8% mass flow at the same volume. Convert units first, then correct for density: mass flow = ρ × Q. For most electronics enclosures the temperature-corrected comparison matters more than the unit conversion itself.

• Convert: m³/h = CFM × 1.699; CFM = m³/h ÷ 1.699.
• Then correct: multiply volume flow by density ratio when temperatures or altitudes differ.
• Pressure: 1 inH₂O = 249 Pa; 1 Pa = 0.00402 inH₂O.

Where the mix-up bites

The failure mode is silent: a European system model quoted at 150 m³/h gets matched against a fan datasheet read as 150 CFM — a 70% shortfall hiding inside identical-looking numbers. Write the unit next to every flow figure in requirement documents, selection emails and test reports, and convert once at the interface between teams rather than in every engineer's head. The same discipline applies to pressure: Pa, inH₂O and mmH₂O all appear in fan documentation, and they are not close to each other.