HVAC Ductwork, Air Handling & Mechanical Products calculator
Fan Motor Power Sizing Calculator
Fan motor sizing converts your airflow and pressure requirements into a shaft power estimate you can use for motor selection. The standard approach multiplies design CFM by total static pressure (in inches water column) and divides by a combined fan efficiency and unit conversion constant. Applying a service factor adds a margin for motor heat, starting loads, and belt losses. The result is an estimated brake horsepower that you round up to the next standard motor frame size before checking the fan performance curve.
What this calculator does
- Estimate the required fan motor shaft power or brake horsepower from design airflow, total static pressure, fan efficiency, and a motor service factor. Use for supply, return, and exhaust fan selection in air handling units and ductwork systems.
- Use this when selecting a supply fan, return fan, or exhaust fan motor for an air handling unit or ductwork system. Enter the design CFM, total static pressure in inches water column, fan total efficiency, and a service factor to get estimated brake horsepower. Round up to the next available motor frame size and confirm with the fan curve.
- Turns design airflow, total static pressure, fan total efficiency into a result for fan motor sizing in hvac ductwork, air handling and mechanical products.
Formula used
- Fan shaft power (BHP) = (CFM × total static pressure) ÷ (6356 × fan efficiency) × service factor
- Round up to the next standard motor size after reviewing the fan curve
Inputs explained
- Design airflow: undefined
- Total static pressure: undefined
- Fan total efficiency: undefined
- Motor service factor: undefined
How to use the result
- Use it when fan motor sizing in hvac ductwork, air handling and mechanical products is being combined into a single number.
- Order of operations and unit alignment matter; this is a simple product, not a unit-aware engine.
Common questions
- How does this fan motor sizing calculator help my hvac ductwork, air handling and mechanical products team? Estimate the required fan motor shaft power or brake horsepower from design airflow, total static pressure, fan efficiency, and a motor service factor. Use for supply, return, and exhaust fan selection in air handling units and ductwork systems. You get a result you can defend before quoting, scheduling, or sign-off.
- Where do I get the inputs for this hvac ductwork, air handling and mechanical products calculator? design airflow, total static pressure, fan total efficiency usually move the result most. Pull from measured hvac ductwork, air handling and mechanical products runs, supplier data, and recent quotes rather than memory.
- How should I act on the output? Use the result as the input to the next hvac ductwork, air handling and mechanical products step or quote line.
- What can throw the result off? Confirm units before you read the number; an off-by-1000 unit error is the usual cause of bad results.
Last reviewed 2026-05-12.