Duct Calculator - HVAC Sizing

Duct Calculator is a focused duct sizing tool for HVAC engineers, designers and installation technicians. Enter what you know and get the duct dimensions, airflow or air velocity you need, without a chart or a slide rule.

CALCULATIONS
- Duct size: find the required duct dimensions from airflow (CFM) and air velocity (FPM).
- Airflow: determine the airflow rate in CFM.
- Air velocity: determine velocity in FPM to help verify system performance.

DUCT SHAPES
- Round ducts
- Rectangular ducts
- Results shown in inches

WHO IT IS FOR
- HVAC engineers and designers checking a duct size during design work.
- Installation technicians and contractors who need a quick answer on site.
- Students learning how airflow, velocity and duct size relate.

WHERE IT HELPS
- Sizing a new supply or return run from a known CFM.
- Checking whether an existing duct keeps velocity within your target.
- Comparing a round duct with a rectangular one when space is tight.

SIMPLE BY DESIGN
A clean interface with only the inputs you need, so you get an answer quickly on the job.

Duct Calculator is free to use. An optional one-time upgrade removes ads.

Results are intended as a calculation aid. Always confirm designs against applicable codes and project requirements.

Download Duct Calculator and size your next duct run.

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