Ductwise: HVAC Duct Calculator

Round and rectangular duct size, CFM, velocity and BTU load in seconds. Imperial or metric. Works offline, no ads, no account.

Size ducts in seconds.

Ductwise is a duct size calculator for HVAC techs and installers. Enter CFM and friction rate to get the round duct size, the rectangular equivalent and the air velocity.

FREE TOOLS

• Duct size (round and rectangular), equal-friction method
• CFM and airflow: from a duct and its velocity, a sensible load, tonnage or air changes
• BTU room load estimate
• Duct velocity (fpm), velocity pressure and friction, checked against your own limit

BUILT FOR THE JOB SITE

• Big, high-contrast numbers you can read at arm's length
• Imperial or metric
• Set your friction rate and max velocity once; every tool starts from them
• Works fully offline, with no ads and no account

DUCTWISE PRO (ONE-TIME PURCHASE)

• Superheat and subcooling for R-410A, R-32, R-454B, R-22, R-134a, R-407C and R-404A
• Size every trunk and branch in one job
• Saved jobs and PDF duct schedule

Pay once. No subscription.

The method is shown on every result, so you can check it against the duct calculator you already carry. Results are guidance; verify against your design standard.