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Duct Air Velocity Calculator

Calculate the air velocity inside a duct given its airflow and cross-sectional area, with typical recommended velocity ranges by application.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Duct air velocity

898.88 ft/min

Check your inputs

Recommended velocity ranges vary by duct application (residential vs. commercial, trunk vs. branch) and are driven by noise, energy, and space constraints rather than a single code-mandated limit — compare your result against your project's design criteria or ASHRAE/SMACNA guidance for the specific duct type.

At the values currently entered, the duct air velocity works out to 899 ft/min. Note that airflow (cfm) and duct cross-sectional area (ft²) sit at the edge of the range this calculator was checked against, so treat the output as indicative rather than settled. Confidence is moderate: the method is sound, but real materials and site conditions vary. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

Add the equipment this sizes

This result is a specification — 898.876 ft/min — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Velocity (ft/min) = Airflow (CFM) ÷ Duct Cross-Sectional Area (ft²), the basic continuity relationship. Typical recommended duct velocity ranges (widely-cited ASHRAE/SMACNA design guidance, not a hard code limit): residential supply trunk ~700-900 fpm, residential branch ~500-700 fpm, commercial main duct ~1000-1500+ fpm — actual limits are set by noise, energy, and space constraints on each specific project.

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Frequently asked questions

How is duct air velocity calculated?
Velocity (in feet per minute) equals the airflow in CFM divided by the duct's cross-sectional area in square feet — the basic continuity relationship between flow rate and area.
What are typical recommended duct velocities?
Widely-cited ASHRAE/SMACNA design guidance puts residential supply trunk ducts around 700-900 fpm, residential branch ducts around 500-700 fpm, and commercial main ducts at 1000-1500+ fpm — these are not hard code limits, and actual limits are set by noise, energy, and space constraints on each specific project.
Why isn't there one universal maximum duct velocity?
Recommended velocity ranges vary by duct application (residential vs. commercial, trunk vs. branch) because they're driven by noise generation, fan energy use, and available duct space rather than a single code-mandated limit — always compare your result against your project's own design criteria.