How to use
How to use the HVAC Duct Calculator
HVAC Duct Calculator is built for contractors who need a practical HVAC duct calculator during estimating, dispatch planning, or proposal review. Use it to turn job details into a clear working number before you finalize pricing in Dabe or your operating system.
When to use this HVAC duct calculator
Use this during duct planning when you need to estimate effective length, round equivalent diameter, velocity, and friction loss.
Step-by-step workflow
Work through the fields in order. The calculator is designed so the most important job inputs come first and supporting assumptions follow after.
- 1.Select metal or flex duct and choose whether you are sizing by friction rate or velocity.
- 2.Enter CFM, duct length, and bend counts so total effective length can be calculated.
- 3.Add a known duct diameter or rectangular sides when you want to evaluate an existing duct instead of solving for a new size.
- 4.Use the utility converters to move between rectangular duct and round equivalent diameter.
How to read the result
The result shows total effective length, equivalent diameter, velocity, and friction loss. Review it against your duct design standards before finalizing scope.
Before you use the number in an estimate
Review the output against your company pricebook, local market, jobsite constraints, and customer expectations. If the result affects equipment sizing, margin, financing, or scope, document the assumptions in the estimate notes so the team can audit the decision later.