HVAC Ductwork Calculator
Use our free HVAC Ductwork Calculator to quickly estimate duct size and airflow, based on key inputs like CFM, air velocity, and friction loss. Perfect for HVAC contractors, engineers, and builders.
Get StartedInput Parameters
Supply: 600-1200 | Return: 400-800 | Exhaust: 800-1500 FPM
Calculation Results
Area (sq ft) = CFM ÷ Velocity
Round Diameter = 2 × √(Area ÷ π) × 12
Rect: Height = √(Area ÷ Ratio) × 12, Width = Ratio × Height
Duct Dimensions
0.00" diameter
Velocity
0 FPM
Duct Area
0.00 sq ft
All calculations are estimates and should be verified by a professional.
HVAC Ductwork Formula
Correct duct sizing ensures proper airflow, energy efficiency, and comfort. Oversized ducts waste money, while undersized ducts create noise and inefficiency.
How this HVAC ductwork calculator works
This calculator uses airflow (CFM), velocity, and friction loss inputs to determine duct dimensions. It applies standard ASHRAE and SMACNA formulas to ensure safe, code-compliant duct sizing for residential and commercial HVAC systems.
When to use this HVAC ductwork calculator
Designing new ductwork layouts for residential or commercial projects
Verifying airflow balance in existing systems
Estimating material needs for duct installation
Comparing round vs. rectangular duct dimensions
Planning energy-efficient HVAC system designs
Want to make your HVAC duct projects smarter?
Use ServiceAgent.ai to automate duct sizing, estimates, proposals, and profitability tracking—all from one dashboard.
Book a Free DemoAverage Profit Margins by Industry
Understand how HVAC ductwork compares to other service industries. Below are typical net margin ranges:
HVAC Contractors
10–20% net margin
Ductwork Fabricators
15–25% net margin
Electrical Contractors
15–25% net margin
Plumbing Contractors
20–35% net margin
Roofing Contractors
20–40% net margin
Cleaning Services
50–70% net margin
Lawn Care
40–60% net margin
General Construction/Contracting
15–30% net margin
These benchmarks help HVAC professionals assess whether ductwork project costs are competitive and profitable.
Frequently Asked Questions
How accurate is this HVAC ductwork calculator?
It provides reliable estimates using industry formulas. Always verify final designs with ASHRAE/SMACNA standards.
What factors affect duct size the most?
Airflow (CFM), velocity limits, duct shape, and friction loss.
Does this calculator support both round and rectangular ducts?
Yes—results are provided for both shapes.
Is this useful for residential and commercial projects?
Absolutely. It works for homes, offices, and large buildings.
Does it account for noise or static pressure?
Indirectly via velocity and friction loss inputs. For precise analysis, use a duct design program.
Can I oversize ducts to reduce noise?
Yes—larger ducts lower velocity and reduce noise but increase cost.
Does this include material or labor costs?
No—it only calculates duct dimensions. Pair with a cost calculator for full estimates.
How does this integrate with my workflow?
Pair it with ServiceAgent.ai to generate automated ductwork layouts, estimates, and project reports.