HVAC Ductulator Calculator

Punch in CFM and friction rate. Get the round size you'll buy, with its real velocity and friction. Pro is a one-time purchase, no subscription.

Size a duct like the paper wheel, in two taps. Enter CFM and your friction rate and get the next standard round size up, with the velocity and the real friction at the size you'll buy.

No fractional answers. Sizes come from the snap-lock, spiral or flex list, and rectangles round up to even inches so the shop can fab them.

The math is the handbook's: ASHRAE Darcy friction with Colebrook, Huebscher equivalents, standard air. Every result shows how it got there.

FREE, NO LIMITS • Size a duct by the equal-friction method, with an optional Manual D velocity limit per run (supply or return, trunk or branch) • Check an existing round or rectangular duct: velocity, friction and equivalent diameter • Round to rectangular for any duct depth, with aspect-ratio warnings past 3:1 and 4:1 • US units (CFM, in, fpm, in/100 ft) or metric (L/s, mm, m/s, Pa/m)

PRO, ONE-TIME PURCHASE • Job sheets: save every sized run to a job and send the office a CSV or PDF takeoff • Friction-rate helper: available static pressure and total effective length in, friction rate out (ACCA Manual D) • Duct board, flex and flat oval, not just galvanized round

Built for installers, service techs and estimators sizing supply and return runs at the truck, in the attic or at the desk. It remembers your last inputs, and it works offline.

Pro is a one-time in-app purchase, not a subscription. Pay once and keep it. It restores on any device signed in to the same Apple ID.

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