Duct Sizing
Estimate round or rectangular duct size from airflow (CFM) and target velocity. A fast duct sizing check for installs, replacements, and comfort fixes.
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Frequently asked questions
Is this a Manual D calculator?
No. This tool estimates duct size using a velocity-target method. Manual D uses friction rate, TEL, and system pressure drops to finalize design.
What inputs matter most?
Airflow (CFM) and your target velocity (FPM). Trunk vs branch and supply vs return influence reasonable velocity targets.
How should I verify the result?
Verify with Manual D / friction charts, equivalent length (TEL), available static pressure, and manufacturer data for equipment, filters, and coils.
Related calculators
- Static Pressure Budget Calculator
- Friction Rate Calculator
- Round ↔ Rectangular Duct Converter
- Air Friction + Velocity Tool
- CFM from BTU / Tons Calculator
- ACH Calculator
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