Horsepower Calculator
This horsepower calculator turns torque and engine speed into horsepower, and works as a torque to hp calculator too. Enter the torque in newton-meters and the RPM and the horsepower calculator gives you power in hp and kW, with the horsepower and torque relationship worked out both ways.
Results
The Horsepower Calculator is part of our Rotation collection. Browse more rotation to size, convert, and check your work alongside this tool.
What the horsepower calculator does
The horsepower calculator finds engine power from torque and rotational speed. Torque is the twist an engine makes; horsepower is how fast it can do that work, and the two are joined by engine speed. As a horsepower and torque calculator it runs both directions, so it also serves as a torque to hp calculator and an engine horsepower estimator.
Horse power formula
The horse power formula is torque times speed. In metric units:
Then kilowatts convert to horsepower by dividing by 0.7457. The 9549 rolls the radians-per-second conversion into one number, and the brake horsepower formula follows the same relationship at the crankshaft.
Horsepower calculator example
A motor making 50 N·m at 3000 RPM, through the horse power formula:
Reverse it and the hp to torque calculator returns 50 N·m from 21.1 hp at 3000 RPM.
How to use the horsepower calculator
Enter the torque in newton-meters and the rotational speed in RPM. The horsepower calculator returns the power in horsepower and kilowatts side by side. To go the other way as an hp to torque calculator, enter the power and RPM and read the torque.
Reading the horsepower calculator result
Notice that power depends on speed as much as twist. The same torque at double the RPM makes double the power, which is why a small engine spinning fast can match a big one turning slowly. Peak horsepower and peak torque almost never happen at the same RPM, a point the horsepower and torque calculator makes clear.
When to use the horsepower calculator
- Rating an engine from bench figures with the horsepower estimator
- Converting torque to hp with the torque to hp calculator
- Checking a drivetrain has enough output
- Estimating engine power with the engine horsepower estimator
Common horsepower mistakes
- Confusing torque with power. High torque at low speed can still be low power.
- Mixing unit systems. Keep torque in newton-meters for the metric horse power formula.
- Expecting peak torque and peak power together. They almost always sit at different RPM.
Tips for accurate horsepower results
- Remember power rises with speed even when torque holds steady.
- Use the torque to hp calculator and its reverse to move between the two.
- Quote the RPM whenever you quote a torque figure.
The link between torque and horsepower
The relationship the horsepower calculator captures is one of the most useful things to carry around any machinery. Power is the product of torque and rotational speed, which means the same power can come from lots of torque turning slowly or a little torque spinning fast. A diesel engine makes its living on the first approach, a motorcycle engine on the second, and both can rate the same horsepower. Once you see power as torque times speed, engine specs stop being a mystery, and the horsepower and torque calculator lets you move between the two freely.
Why gearing and the horse power formula work together
Gearing cannot create power, but it can trade one part of the horse power formula for the other. Reduce the speed through a gear set and the torque rises in step, which is how a small high-revving motor drives a heavy load: it makes modest torque at high RPM, and the gears convert that into large torque at low RPM while the power stays roughly the same. When you run the horsepower calculator and the number looks low for the torque, check the RPM; when the torque looks small for the power, the speed is doing the work.
Horsepower reference chart
Power at common torque and RPM from the horsepower calculator:
| Torque | RPM | Power |
|---|---|---|
| 50 N·m | 1500 | 10.5 hp |
| 50 N·m | 3000 | 21.1 hp |
| 100 N·m | 3000 | 42.1 hp |
Horsepower Calculator FAQ
What is the horse power formula?
In metric units, kW = torque × RPM ÷ 9549, then hp = kW ÷ 0.7457. The horsepower calculator applies this horse power formula and shows both hp and kW.
How do I convert torque to hp?
Multiply torque by RPM and divide by the constant, then convert to hp. The torque to hp calculator does it, and the hp to torque calculator reverses it.
What is the difference between torque and horsepower?
Torque is the turning force; horsepower is the rate of doing work, which folds in engine speed. The horsepower and torque calculator shows how they relate at any RPM.
What is brake horsepower?
Brake horsepower is the power measured at the crankshaft. The brake horsepower formula uses the same torque and RPM relationship this horsepower calculator applies.