Horsepower Calculator Online
Calculate horsepower from torque and RPM, or convert between horsepower and kilowatts, entirely on your device.
The Horsepower Calculator runs entirely in your browser. The torque, RPM, and power values you enter are never uploaded to ArrayKit.
Open the Engine Horsepower Calculator
About Horsepower Calculator
Horsepower Calculator turns torque and engine speed into horsepower using the same hp = torque × RPM ÷ 5252 formula dyno sheets and engine builders rely on. Enter torque in pound-feet and RPM in the Torque & RPM mode to get horsepower and kilowatts instantly, or switch to Unit convert to move a single power figure between horsepower and kilowatts without touching torque at all. It is useful for checking a dyno printout, comparing an engine build against a manufacturer's rated output, sizing a generator or motor listed in kW, or settling a quick hp-versus-kW argument. Built for gearheads, mechanics, and engineering students who want an instant, accurate figure without pulling out a formula sheet. Everything runs locally in your browser — the numbers you enter are never uploaded.
Features
- Solve horsepower and kilowatts from torque (lb-ft) and RPM
- Uses the standard hp = torque × RPM ÷ 5252 dyno formula
- Unit convert mode moves a single figure between horsepower and kilowatts
- Shows torque and RPM alongside the solved horsepower for reference
- Instant recalculation as you type — no submit button needed
- Copy a plain-text summary of horsepower, kilowatts, and torque
- Clear error message when torque or RPM is missing or negative
- Runs entirely in your browser — your figures are never sent anywhere
How to use the Horsepower Calculator
- Choose Torque & RPM or Unit convert
- Enter torque in pound-feet and engine speed in RPM (or a single hp/kW value)
- Read the solved horsepower and kilowatts
- Copy the summary or switch modes to check another figure
Example
Input
400 lb-ft @ 5252 rpm
Output
400 hp (298 kW)
At exactly 5252 RPM, torque in lb-ft and horsepower are always numerically equal.
Common errors & troubleshooting
- Horsepower looks much higher or lower than the engine's spec sheet. — Double-check torque is in pound-feet, not Newton-meters — the Horsepower Calculator's formula expects lb-ft, so a Nm figure needs converting first (divide Nm by 1.3558 to get lb-ft).
- Result shows an error after entering torque and RPM. — Make sure both fields are plain numbers of 0 or more — the Horsepower Calculator needs a positive torque and RPM to solve for horsepower.
- Converted kilowatts figure seems slightly off from another source. — The Horsepower Calculator uses 1 hp ≈ 0.7457 kW (mechanical horsepower), which can differ slightly from metric horsepower (PS) conversions used by some manufacturers.
- Torque and horsepower show the same number and it looks like a bug. — That is expected at 5252 RPM — the dyno formula makes lb-ft torque and horsepower cross at that exact engine speed, above which horsepower exceeds torque and below which it trails it.
Frequently asked questions
- How does the Horsepower Calculator turn torque and RPM into hp?
- It applies the standard formula horsepower = torque (lb-ft) × RPM ÷ 5252, the same relationship used on dyno printouts, so the horsepower and torque curves always cross at 5252 RPM.
- Can the Horsepower Calculator convert kilowatts to horsepower?
- Yes. Switch to Unit convert, enter a value in kW, and the calculator returns the equivalent horsepower using 1 hp ≈ 0.7457 kW — or enter hp to get kilowatts instead.
- What units does the Horsepower Calculator expect for torque?
- Torque & RPM mode expects torque in pound-feet (lb-ft) and RPM as a whole number. If your torque figure is in Newton-meters, divide it by about 1.3558 first to convert to lb-ft.
- Is the Horsepower Calculator's result exact for a real engine?
- It is an estimate based on the standard torque-to-horsepower formula at a single RPM point, not a full dyno run — verify against your engine's actual dyno sheet or manufacturer specs before relying on it for tuning or purchasing decisions.
- Does the Horsepower Calculator upload the numbers I enter?
- No. The Horsepower Calculator computes everything locally in your browser. The torque, RPM, and power values you enter are never uploaded to ArrayKit.
- Why do horsepower and torque match at 5252 RPM?
- It is a mathematical artifact of the formula's constant: hp = torque × RPM ÷ 5252 always produces hp = torque when RPM equals 5252, regardless of the engine, so every dyno chart crosses at that exact speed.
Related tools
All ArrayKit tools