Duct Sizing Calculator

Overview

A web-based calculator to help size HVAC ductwork. You pick what you want to solve for (velocity, cross-sectional area or flow rate) and it asks only for the inputs that answer needs.

Duct sizing comes down to one relationship between airflow, area and velocity, but the inputs show up in a mix of units on real projects. The calculator handles that conversion and, when solving for area, suggests the best duct size for the conditions.

What it does

• Choose the answer: solve for velocity, cross-sectional area or flow rate, and the input form changes to match.
• Any units in: enter airflow, duct dimensions or flow in the units you have, and get results in the units you need (CFM, m/s, square inches and so on).
• Optimal sizing: when solving for area, it works out the most suitable duct size for the given parameters.

What I'd add next

• Duct tees: flow split and sizing where branches and T-junctions come off the main run.
• Friction losses: duct friction loss, so the sizing reflects real pressure drop and not just velocity.