Free horsepower calculator

Horsepower calculator torque, RPM, kW and PS

Get horsepower from torque and engine speed, the torque behind a horsepower figure, or convert between horsepower, kilowatts and metric horsepower (PS).

Free, no sign-upRuns in your browserNothing is uploaded
What do you want to work out?

Why 5,252: one horsepower is 33,000 lb·ft of work a minute, and one revolution turns a lb·ft of torque through 2π radians, so hp = torque × RPM × 2π ÷ 33,000 = torque × RPM ÷ 5,252.1. That's also why torque and horsepower curves cross at 5,252 RPM.

Horsepower-
-

In short

Horsepower = torque in lb·ft × RPM ÷ 5,252. The 5,252 is 33,000 ÷ 2π: one horsepower is 33,000 lb·ft of work a minute, and each revolution is 2π radians. So 400 lb·ft at 5,252 RPM is 400 hp. One mechanical horsepower is 745.7 watts and one metric horsepower (PS) is 735.5 watts, so 300 hp is 223.7 kW or 304.2 PS.

How it works

How to use the Horsepower Calculator

1

Pick a calculation

Torque to horsepower, horsepower to torque, or a power unit conversion.

2

Enter the figures

Torque in lb·ft or N·m and the RPM, or power in hp, kW or PS.

3

Read every unit

Horsepower, kilowatts, metric hp and torque in lb·ft and N·m.

What it does

What the horsepower calculator works out

Torque to horsepower

lb·ft or N·m at any RPM.

Horsepower to torque

The torque a horsepower figure needs at a given RPM.

hp, kW and PS

Mechanical horsepower, kilowatts and metric horsepower, with NIST factors.

The 5,252 explained

Why the torque and horsepower curves cross at 5,252 RPM.

Private

Runs in your browser. Nothing is uploaded.

Horsepower
lb·ft × RPM ÷ 5,252.11 (33,000 ÷ 2π)
Torque
hp × 5,252.11 ÷ RPM
1 hp
550 ft·lbf/s = 745.69987 W (NIST SP 811: 745.6999)
1 PS (metric hp)
75 kgf·m/s = 735.49875 W (NIST SP 811: 735.4988)
Metric torque
kW = N·m × RPM ÷ 9,549.3
FAQ

Questions about the horsepower calculator

How do you calculate horsepower from torque?
Multiply torque in lb·ft by RPM and divide by 5,252. 350 lb·ft at 4,000 RPM is 350 × 4,000 ÷ 5,252 = 266.6 hp.
Why is the number 5,252?
One horsepower is 550 ft·lbf a second, or 33,000 lb·ft of work a minute. Torque does work through an angle, 2π radians per revolution, so hp = torque × RPM × 2π ÷ 33,000, and 33,000 ÷ 2π = 5,252.1.
How many kW is one horsepower?
One mechanical horsepower (550 ft·lbf per second) is 0.7457 kW, so multiply hp by 0.7457. One kW is 1.341 hp.
What's the difference between hp and PS?
PS is metric horsepower, 75 kgf·m per second, or 735.5 W. It's about 1.4% smaller than a mechanical horsepower, so 100 hp is 101.4 PS.
Is wheel horsepower the same as engine horsepower?
No. Published engine figures are measured at the crank; a chassis dyno measures at the wheels, after the transmission and axle, so it reads lower.
Keep going

Guides and features for this

Torque unit converterBayRobinEngine displacement calculatorBayRobinTransmission shopsBayRobinGeneral auto repair shopsBayRobinAll guides on running an auto repair shopTopic guides
Sources

Where the formulas and rules come from

Checked October 2026. Conversion factors from the unit definitions (NIST SP 811). Dyno results vary with the dyno and conditions.

Link to this tool

Useful for your team or your readers? Paste this into a blog post, forum or resource page.

More free shop tools

All free tools
Gear Ratio CalculatorFree gear ratio calculatorEngine Displacement CalculatorFree displacement calculatorCompression Ratio CalculatorFree compression ratio calculatorEffective Labor Rate CalculatorFree labor rate calculatorParts Markup CalculatorFree parts pricing calculatorRepair Order Gross Profit CalculatorFree RO profit calculator

Never miss a service call

BayRobin's AI receptionist answers every call with your shop's name, gets the concern and the year, make and model, and books the appointment into your schedule. Free until your first 10 booked jobs, no card up front.

Start freeSee the AI receptionist