About this calculator

Most homes need 1 CFM per 1–2 ft² of floor. Round duct diameter (in) ≈ √(CFM ÷ 6) for typical 700 fpm velocity.

Frequently asked questions

What does the Duct CFM & Size Calculator do?

Required airflow and duct diameter for a room. Most homes need 1 CFM per 1–2 ft² of floor. Round duct diameter (in) ≈ √(CFM ÷ 6) for typical 700 fpm velocity.

Is the Duct CFM & Size Calculator free to use?

Yes. Every calculator on Calcurly.com is free, works in your browser without sign-up, and can be embedded on your own website.

How accurate is the Duct CFM & Size Calculator?

Results are calculated in real time using industry-standard formulas. Treat the output as a well-informed estimate — always cross-check with local regulations, product datasheets, or a qualified hvac & climate professional before committing to a purchase or a job.

What inputs does the Duct CFM & Size Calculator need?

Enter values for: Floor area (ft²), ft² per CFM. Sensible defaults are pre-filled where possible so you can start with a single change.

Can I embed the Duct CFM & Size Calculator on my own website?

Yes — copy the iframe snippet at the bottom of this page, or use the Embed Generator to customise the size. The embedded version stays in sync with the live calculator on Calcurly.com.