Calculated result
240CFM
Planning airflow
Formula
HVAC-CFM-001CFM = length × width × height × ACH ÷ 60
2400 ft³
Room volume
6 ACH
Air changes per hour
113.27 L/s
L/s
HVAC calculator
CFM calculator
a 20 × 15 × 8 ft room at 6 air changes per hour returns 240 CFM. In metric, room volume is 67.96 m³.
Formula. CFM = length × width × height × ACH ÷ 60
Planning airflow from room volume and air changes per hour. Not a duct design or Manual D.
By Feroz Sheikh · Formula HVAC-CFM-001 v1.0.0 · Tested formula
Formula
HVAC-CFM-001v1.0.0Project inputs
Enter your measurements. Switching units converts the same project, including coverage and unit rates. Package yields keep the unit printed beside each field.
Refine measurements and rates at any time. Your current values are included in the material-list PDF.
Planning estimate, not engineering advice. Confirm site measurements and product specifications. Calculation limits.
Planning CFM is room volume times air changes per hour, divided by 60. Not a duct design or Manual D.
- Measure the room that will be supplied, not the whole floor unless you mean that.
- ACH is a planning input. Occupied rooms, shops and toilets do not share a number.
- Duct size, static pressure and the fan curve stay with the designer.
Add your project costs
Add rates if you are pricing a related project line. Pick a currency — badges, inputs, and totals follow.
This page is geometry, not a material takeoff. Leave rates at zero unless you are pricing a related line. Construclytic does not fetch supplier prices.
How this calculator works
A transparent cfm takeoff.
Feroz SheikhWritten by Feroz Sheikh · founder
Planning CFM is room volume times air changes per hour, divided by 60. Not a duct design or Manual D.
HVAC-CFM-001 is planning airflow: room volume × air changes per hour ÷ 60. A 20 × 15 × 8 ft room at 6 ACH is 240 CFM. Not Manual D, not a duct size, not register throw and not a ventilation-code path.
Worked example. Example: a 20 × 15 × 8 ft room at 6 air changes per hour returns 240 CFM.
See the example inputs and calculated result
This separate example uses the calculator's starting values in imperial units. It stays unchanged when you edit the tool above. Example rates, yields and dimensions are assumptions, not recommendations for your project.
| Input | Example value |
|---|---|
| Room length | 20 ft |
| Room width | 15 ft |
| Ceiling height | 8 ft |
| Air changes per hour | 6 ACH |
Example result: Planning airflow — 240 CFM.
CFM = length × width × height × ACH ÷ 60
Use the labelled units above when reproducing this example. To work in metric, switch the calculator to Metric; applicable measurements are converted, while product-specific units remain labelled.
- 1. Measure the room that will be supplied, not the whole floor unless you mean that.
- 2. ACH is a planning input. Occupied rooms, shops and toilets do not share a number.
- 3. Duct size, static pressure and the fan curve stay with the designer.
Field notes that change the number
- Measure the room that will be supplied, not the whole floor unless you mean that.
- ACH is a planning input. Occupied rooms, shops and toilets do not share a number.
- Duct size, static pressure and the fan curve stay with the designer.
Common mistakes
- Using 6 ACH as if it were a code number.
- Sizing ducts from this CFM alone.
- Treating this as a balanced-ventilation or Manual D design.
Need the broader workflow? Read the hvac planning guide.
How-to: How to plan a furnace BTU load
Questions
Questions about cfm
Is 6 ACH a code number?
It is a common occupied-room start, not a ventilation-code path.
Does this size ducts?
No. Manual D, friction rate and register throw are not on this page.
What is the formula ID?
This cfm calculator publishes formula HVAC-CFM-001, version 1.0.0. The ID stays on the result and on the estimate line.