Duct area & measured air velocity

MEASURE FIRST

How to prepare your inputs

Measure room dimensions and use airflow measured at the outlet. A catalogue free-air fan rating is not necessarily installed airflow.

How this calculation works

Area = π × (diameter ÷ 1,000)² ÷ 4. Average velocity = airflow ÷ 1,000 ÷ area.

Assumptions & exclusions

Arithmetic only. Does not recommend velocity, size a duct/fan, estimate pressure losses, noise or balancing. Use internal dimensions and actual measured installed flow.

Your next step

Ask an HVAC specialist for heat-load, airflow and duct design. Room volume alone does not size an air conditioner.

Further reading

• Blocklayer geometric tool directory

These resources provide background information. Confirm current product specifications and project requirements with your supplier or trade professional.

What if my shape or product is different?

Use dimensions and product data that match the stated method. For complex work, calculate separate sections or obtain a project-specific take-off. Do not apply simple geometry to structural or compliance decisions.

Why are quantities rounded up?

Whole bags, packs, sheets or cartridges round up to purchasable units. Decimal area or volume results are planning figures; confirm order increments with the supplier.

Are my entries saved?

No. Entries remain in the current browser page and clear on reload. Printing can save your results and inputs as a PDF on your device.