// multi-utility computation suite · offline · instant · precise
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eng.hvac-duct-sizing Calculator
Calculates HVAC duct size for a given airflow and design velocity or pressure drop using the equal friction method. Supply air ductwork is typically sized at 0.08 in.w.g./100 ft (0.9 Pa/m) velocity pressure — oversized ducts reduce pressure drop but increase material cost.
Inputs
Airflow Cfm
Reference formula or conversion factor shown for context.
Friction Rate In Per 100Ft
Amount per unit of time or per unit quantity. Check the denominator before interpreting.
Duct Type
Reference formula or conversion factor shown for context.
Aspect Ratio
Reference formula or conversion factor shown for context.
Results
round duct diameter (in)
The computed diameter -- twice the radius.
rectangular: width × height (in)
The computed height.
air velocity (fpm)
Reference formula or conversion factor shown for context.
velocity check
A pass/fail verification against the applicable code, standard, or threshold.
friction rate
The value at the specified point or condition.
supply duct max
Reference formula or conversion factor shown for context.