Duct Calculator
Use our free Duct Calculator to quickly estimate duct size and airflow requirements, based on key inputs like CFM, velocity, and friction loss. Perfect for HVAC contractors and homeowners.
Duct Sizing Formula
Proper duct sizing ensures balanced airflow, system efficiency, and comfort. Undersized ducts create noise and pressure drops; oversized ducts waste material and cost. Skip manual math—use our free Duct Calculator for instant results.
How this duct calculator works
This calculator estimates duct size using airflow (CFM), velocity, and friction loss inputs. It applies standard HVAC design formulas to ensure accurate duct sizing for residential or commercial projects.
When to use this duct calculator
Designing HVAC ductwork for new installations
Checking airflow balance during renovations
Comparing duct sizes for different HVAC system loads
Troubleshooting airflow or comfort issues
Planning material costs and labor for ductwork projects
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Average Profit Margins by Industry
Understand how HVAC ductwork compares to other service industries. Below are typical profit margin ranges across common service businesses:
HVAC Contractors
Ductwork Fabricators
Plumbing Contractors
Electrical Contractors
Roofing Contractors
Construction/Contracting
These benchmarks help HVAC professionals evaluate whether duct installation costs are competitive and profitable.
Frequently Asked Questions
It uses industry-standard airflow and velocity formulas to provide reliable estimates. Final designs should follow ASHRAE or SMACNA guidelines.
Key drivers include airflow (CFM), air velocity, static pressure, and friction loss.
Yes—this calculator provides area and diameter. Rectangular equivalents can be sized from the same values.
Absolutely. It provides quick estimates for proposals and installations.
Yes—enter velocity values that match your design standards.
No—it only calculates duct size. Add labor and material costs separately.
Yes—just input the appropriate airflow and velocity for the project type.
Pair it with ServiceAgent.ai to streamline duct sizing, quotes, and project management.