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CFM Calculator

This CFM calculator finds airflow in cubic feet per minute and converts it to m³/h. Example: a room of 20 × 15 × 8 ft with 6 air changes per hour needs 240 CFM, about 407.76 m³/h.

Example: Unit system: Imperial (ft, ft², ft/min) · Calculation: From room volume and air changes · Room length 20 ft / m · Room width 15 ft / m · Room height 8 ft / m · Air changes per hour 6 1/h → Result: 240 CFM = 407.763 m³/h = 113.267 L/s. Source: NIST SP 811 – conversion factors: 1 ft = 0.3048 m and 1 ft³ = 0.028316846592 m³ (exact). Updated: .

ft / m
In ft (imperial) or m (metric).
ft / m
In ft (imperial) or m (metric).
ft / m
In ft (imperial) or m (metric).
1/h
How many times per hour the room air is replaced completely.
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Result

Result
240 CFM = 407.763 m³/h = 113.267 L/s
Airflow in all units
UnitValue
CFM (ft³/min)240
m³/h407.763
L/s113.267
m³/min6.79604
Calculation steps
  • Room volume V = L · W · H = 20 · 15 · 8 ft = 67.9604 m³.
  • Airflow Q = V · air changes / time = 67.9604 m³ · 6 per hour = 407.763 m³/h = 240 CFM.
  • Conversion: 1 CFM = 0.028316846592 m³/min ≈ 1.69901 m³/h ≈ 0.471947 L/s (1 ft = 0.3048 m, exact).
CFM (cubic feet per minute) is a US measure of airflow. The calculator gives a guideline value; design and standards for ventilation systems must be checked separately.

How it is calculated

CFM stands for cubic feet per minute and states how many cubic feet of air flow per minute through a fan, duct or room. The unit is common in the US for fans, air conditioners and extraction systems; in Europe airflow is usually given in m³/h or L/s.

Two ways to calculate

From air changes: room volume times air changes per hour, divided by 60, gives CFM when the volume is in ft³. From a duct: Q = A · v, cross-sectional area times air velocity. For conversion, 1 ft³ = 0.028316846592 m³, so 1 CFM ≈ 1.699 m³/h.

Worked example

A room measures 20 × 15 × 8 ft = 2400 ft³. At 6 air changes per hour that is 14,400 ft³ per hour or 240 ft³ per minute, so 240 CFM. That equals 240 · 1.69901 ≈ 407.76 m³/h or about 113.27 L/s. Air moving at 500 ft/min through a 2 ft² duct gives 2 · 500 = 1000 CFM.

Frequently asked questions

How do you convert CFM to m³/h?

Use the factor 1.69901: m³/h = CFM · 1.69901. 1000 CFM is about 1699 m³/h.

How do you calculate the CFM needed for a room?

Room volume in ft³ times the desired air changes per hour, divided by 60. In the example 2400 ft³ · 6 / 60 = 240 CFM.

What is the difference between CFM and m³/h?

Both are airflow rates: CFM in cubic feet per minute, m³/h in cubic metres per hour. 1 CFM equals about 1.699 m³/h.

Sources and legal basis

As of: · Editorial policy

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