HVAC Duct Size Calculator
Calculate duct size, airflow (CFM), air velocity, and pressure drop for residential and commercial HVAC systems. Based on ASHRAE friction chart standards for US contractors and engineers.
ΔP = f × (L/D) × (ρV²/2)
Area (round) = π × (D/24)² · Velocity = CFM ÷ Area
- Duct Shape—
- Cross-Section Area—
- Hydraulic Diameter—
- Perimeter—
- Airflow (CFM)—
- Air Velocity—
- Friction Rate—
- Pressure Drop / 100 ft—
- Total Pressure Drop—
- Enter values to see recommendations
Maximum recommended air velocities by application type per ASHRAE Handbook — HVAC Systems and Equipment.
| Application | Duct Type | Velocity (FPM) | Pressure | Noise Level |
|---|---|---|---|---|
| Residential Supply | Main Trunk | 700–900 | Low | Quiet |
| Residential Return | Return Trunk | 600–700 | Low | Quiet |
| Residential Branch | Supply Branch | 400–600 | Very Low | Quiet |
| Commercial Supply | Main Trunk | 1000–1500 | Medium | Moderate |
| Commercial Return | Return Trunk | 800–1200 | Medium | Moderate |
| Commercial Branch | Supply Branch | 600–900 | Low | Moderate |
| High-Velocity Supply | Main Trunk | 2000–2500 | High | Loud |
| Industrial Exhaust | Exhaust | 2500–4000 | Very High | Very Loud |
| Kitchen Exhaust | Exhaust Hood | 1500–2500 | High | Loud |
| Clean Room / Lab | Supply | 300–600 | Very Low | Very Quiet |
Hvac Duct Calculator
Welcome to All Types Calculators – your easy-to-use online solution for quick and accurate HVAC calculations.
Our HVAC Duct Calculator helps you determine the correct duct size for heating and cooling systems without complex manual formulas. Whether you are an HVAC technician, engineer, contractor, or student, this tool makes duct sizing simple, fast, and reliable.
What is an HVAC Duct Calculator?
An HVAC duct calculator is a tool used to estimate the correct size of air ducts based on airflow, duct length, friction loss, and system pressure.
It helps ensure that air moves smoothly through the system without unnecessary resistance or energy loss.
With the HVAC Duct Calculator, you can avoid:
- Uneven cooling or heating
- Excess noise in ducts
- High electricity bills
- Poor airflow in rooms
- Extra load on HVAC systems
How HVAC Duct Calculator Works
Our tool uses standard HVAC principles to estimate duct size based on your inputs.
Enter Airflow (CFM): You provide the required airflow for your space in cubic feet per minute (CFM).
Select Duct Type: Choose between round or rectangular duct options depending on your system design.
Enter System Details:
- Total duct length
- Friction loss rate
- Number of bends (45°, 90°, 180°)
Get Fast Results
The calculator quickly shows the recommended duct size for optimal airflow.
Who Should Use This Tool?
- HVAC technicians
- Mechanical engineers
- Contractors
- Students learning HVAC design
- Homeowners planning HVAC installation
Frequently Asked Questions
Can wrong duct size affect HVAC performance?
Yes, incorrect duct size can cause poor airflow, uneven heating or cooling, higher energy bills, and extra strain on the HVAC system.
What units are used in HVAC duct calculations?
Common units include:
- CFM (Cubic Feet per Minute) for airflow
- Inches of water gauge (in/wg) for pressure
- Feet for duct length
- Inches for duct diameter
Is this HVAC Duct Calculator free to use?
Yes, the HVAC Duct Calculator on All Types Calculators is completely free and can be used anytime without registration.