HVAC Ductwork Size Calculator
Round duct diameter needed for an airflow and target friction rate.
Compare Your Options And Get Clear Answers
Round duct diameter needed for an airflow and target friction rate.
HVAC Ductwork Size Estimator
Enter your numbers below for an instant estimate.
How It Works
Key concepts behind this calculator
Enter Values
Fill in each field with your own numbers.
Calculate
Results update as you change the inputs.
Review
Read the breakdown and the explanation.
Adjust
Change values to compare scenarios.
HVAC Quick Guide
Typical values for reference.
| CFM | fpm | Shape | Diameter |
|---|---|---|---|
| 400 | 700 | 1 | 10.2 in |
| 100 | 600 | 1 | 5.5 in |
| 1200 | 900 | 1 | 15.6 in |
| 250 | 700 | 2 | 8.1 in |
| Rule of Thumb | Check inputs | Use as a guide | Round sensibly |
HVAC Ductwork Size Calculator FAQ
Answers to common questions about this calculator.
It uses the formula shown with your inputs. Real prices and rules vary, so treat it as a guide.
Area = CFM / velocity.
It is an estimate based on the inputs you enter. Check real quotes, labels or official guidance for important decisions.
Yes. Replace each input with your own figures and the result updates instantly.