Duct Pressure Drop Calculator
Use this preliminary HVAC calculator to estimate duct velocity, friction loss, equivalent length, and total pressure drop for ductwork design.
This tool is intended for preliminary reference only. Final ductwork sizing and fan selection should be verified by a qualified mechanical professional and applicable design standards.
What This Calculator Will Help Estimate
- Air velocity in ductwork
- Duct area
- Friction loss per 100 ft
- Equivalent length for fittings
- Total duct pressure drop
- Preliminary fan external static pressure allowance
Typical Inputs
- Airflow, CFM
- Duct type: round or rectangular
- Duct width and height, or round duct diameter
- Duct length
- Fitting quantity and equivalent length
- Friction rate or design velocity
Basic Formula References
Duct Area:
Area = Width × Height for rectangular duct, or πD² / 4 for round duct.
Velocity:
Velocity = Airflow / Area
Total Pressure Drop:
Total Pressure Drop = Straight duct friction loss + fitting pressure loss + equipment/accessory losses.
Download the Excel Calculator
Use the downloadable Excel workbook to estimate duct velocity, straight-duct friction loss, fitting equivalent length, and preliminary total pressure drop.
This workbook is intended for preliminary design reference. Final duct sizing and equipment selection should be verified based on the project requirements and applicable codes.
Download Duct Pressure Drop Calculator
Need Project-Specific Engineering Support?
Submit your project information for a duct-pressure-drop review, HVAC design support, or a broader mechanical-system assessment.