CFM Conversion Calculator — m³/h, CMH, CMM, L/s & CFH

Divide m³/h by 1.699011. For example, 29 m³/h ÷ 1.699011 = 17.1 CFM, and 600 m³/h ÷ 1.699011 = 353 CFM. Going the other way, multiply CFM by 1.699011: a 100 CFM bathroom fan is 169.9 m³/h on a European datasheet. The calculator above converts both directions live with the exact factor.

Multiply CFM by 1.699011 (or 1.699 if two decimals are enough). 100 CFM × 1.699011 = 169.9 m³/h; 250 CFM = 424.8 m³/h; 1,200 CFM = 2,038.8 m³/h. The factor is exact: one foot is 0.3048 m by definition, so one cubic foot is 0.028316846592 m³, times 60 minutes = 1.69901077552 m³ per hour per CFM.

CMH (cubic meters per hour) is the same unit as m³/h, so the factor is identical: divide CMH by 1.699011. A fan listed at 170 CMH is 170 ÷ 1.699011 = 100.1 CFM; 500 CMH is 294.3 CFM. Watch datasheets that write 'CMH' but mean m³/h at a specific static pressure — always compare ratings at the same pressure.

One CMM (cubic meter per minute) equals 35.3147 CFM, so multiply CMM by 35.3147 — or divide CFM by 35.3147 to get CMM. Example: 2.83 CMM × 35.3147 = 100 CFM, and 100 CFM ÷ 35.3147 = 2.83 CMM. CMM appears on some Asian blower specs; it is just m³/h ÷ 60.

Multiply liters per second by 2.11888 to get CFM, or divide CFM by 2.11888 to get L/s. (Equivalently: CFM × 0.471947 = L/s.) A 40 L/s UK extract fan is 40 × 2.11888 = 84.8 CFM; a 100 CFM fan is 47.2 L/s. UK building regulations quote extract rates in L/s, which is why the factor matters there.

Divide liters per minute by 28.316846592, or multiply CFM by that factor to get LPM. Example: 2,832 LPM ÷ 28.3168 = 100 CFM, and a 400 CFM inline fan moves 11,327 LPM. LPM is the same unit as L/s × 60 — if a spec lists both and they do not differ by exactly 60, the sheet has a typo.

40 L/s × 2.11888 = 84.8 CFM. That is the UK's typical whole-dwelling minimum extract on boost for a mechanical ventilation system, and it converts to 144 m³/h. Reverse check: 84.8 CFM × 0.471947 = 40.0 L/s — the factors close perfectly because they derive from the same definition of the foot.

29 m³/h ÷ 1.699011 = 17.1 CFM. That figure appears on compact EU ERV/HRV units and small continuous-extraction fans. It converts to 8.06 L/s or 480.7 L/min — enough for a small utility room's background ventilation, not for a bathroom boost requirement.

CFH is cubic feet per hour — CFM × 60. To convert CFH to CFM, divide by 60: 3,600 CFH = 60 CFM. You will meet CFH on older US gas-appliance vent tables, burner combustion-air ratings, and some compressor specs. Modern HVAC paperwork has largely moved to CFM or m³/h, but the unit is still current in plumbing and gas work.

It follows each region's building-ventilation standards. Continental European fan manufacturers rate products in m³/h because ISO airflow conventions and EU energy labels are built on it. UK building regulations (Approved Document F) specify extract rates in liters per second, so UK fans, testers and spec sheets follow in L/s. When equipment crosses borders, this calculator's factor table keeps quotes comparable.

Exactly 1.69901077552 m³/h — the decimal comes from the international foot definition (1 ft = 0.3048 m exactly). Rounding to 1.699 introduces 0.0006% error; rounding to 1.7 introduces 0.06%, which compounds to a visible drift only above ~5,000 CFM (a 1,000 CFM fan converted with 1.7 reads 1 m³/h high). The calculator uses the full precision and displays rounded results.

The unit conversion does not — 100 CFM is 169.9 m³/h at any pressure — but the fan's actual output does. A fan rated 100 CFM at 0.1 in. w.c. may deliver 70 CFM at 0.3 in. w.c., and 70 CFM is 118.9 m³/h. Convert the delivered number, not the free-air nameplate, when comparing against a metric-rated system requirement.