HVAC Unit Converter
Imperial ↔ metric conversions for the numbers that show up on duct drawings, fan curves and submittals.
Enter a value, then select Calculate.
A fan curve from a European manufacturer shows 3,400 m³/h at 250 Pa, and the drawing set is in CFM and inches of water.
- 1
Convert the airflow
3,400 m³/h ÷ 1.699 = 2,001 CFM
1 CFM = 1.699 m³/h exactly as defined here.
- 2
Convert the static pressure
250 Pa ÷ 248.84 = 1.00 in. w.g.
A coincidence worth remembering: 250 Pa is almost exactly 1 in. w.g.
- 3
Sanity-check against the fan table
2,000 CFM @ 1.0 in. w.g. → compare with the US-rated curve at the same point
Conversions change units, not density — altitude corrections are a separate step.
Takeaway: Convert at the start of a comparison, not at the end — mixing CFM and m³/h mid-calculation is how a 70% airflow error slips into a submittal.
Method and assumptions
- 1 CFM = 1.699 m³/h = 0.4719 L/s. 1 in. w.g. = 248.84 Pa (water at 60 °F). 1 m/s = 196.85 FPM. 1 in = 25.4 mm (exact).
- Pressure conversions are unit conversions only — they do not correct for air density, altitude or temperature.
- Results rounded for display: whole units above 1,000, one decimal above 100, three decimals above 1, five below.
This calculator is for preliminary design guidance only. Final duct sizing, construction, and installation must be performed by qualified professionals and comply with applicable codes and standards.