CFM by Room Size Chart
Airflow in cubic feet per minute for rooms from 8 to 30 feet long at a 12 ft width and 8 ft ceiling, at four air changes an hour. Multiply by two for a kitchen or bathroom and by three where there are fumes.
Source data and formula checked · How we check
CFM by Room Size Chart reads airflow needed straight off room length, for 12 values from 8 to 30. Every row is computed from the same formula the calculator uses, not measured or copied from another table, so a value between two rows can be worked out the same way. The formula is the one published by ASHRAE Standard 62.2.
At four air changes an hour, the rate for a living room or bedroom.
| Room length (ft) | Airflow needed | Room volume | Bathroom rule of thumb, 1 CFM per sq ft |
|---|---|---|---|
| 8 | 51 CFM | 768 cu ft | 96 CFM |
| 10 | 64 CFM | 960 cu ft | 120 CFM |
| 12 | 77 CFM | 1,152 cu ft | 144 CFM |
| 14 | 90 CFM | 1,344 cu ft | 168 CFM |
| 16 | 102 CFM | 1,536 cu ft | 192 CFM |
| 18 | 115 CFM | 1,728 cu ft | 216 CFM |
| 20 | 128 CFM | 1,920 cu ft | 240 CFM |
| 22 | 141 CFM | 2,112 cu ft | 264 CFM |
| 24 | 154 CFM | 2,304 cu ft | 288 CFM |
| 26 | 166 CFM | 2,496 cu ft | 312 CFM |
| 28 | 179 CFM | 2,688 cu ft | 336 CFM |
| 30 | 192 CFM | 2,880 cu ft | 360 CFM |
Questions people actually ask
- How do I read the CFM by Room Size Chart?
- Find your room length in the first column and read across. At 8 ft the airflow needed is 51 CFM; at 30 ft it is 192 CFM. The table runs from 8 ft to 30 ft in 12 rows.
- How much does the airflow needed change per row?
- By 13 CFM for every 2 ft of room length, and by the same amount everywhere in the table — the relationship is a straight line, so halfway between two rows is halfway between their two answers. That is what makes reading between the rows safe here.
- What if my room length is outside the table?
- The chart covers 8 ft to 30 ft, which is the range people actually look up. Anything above or below goes into the calculator, which takes any figure and shows each step of the working rather than only the result. Open the cfm calculator.
- Where do these numbers come from?
- Every row is computed at build time from the formula published by ASHRAE Standard 62.2, by the same code behind the calculator — not transcribed from another table, which is how a rounding error in one chart ends up in twenty.
Need a different number?
The chart covers the common values. For anything between the rows, the cfm calculator takes any figure and shows the working.
Source: ASHRAE Standard 62.2 — ventilation in residential buildings, US EPA — indoor air quality