Want to know how much power your engine really makes? Just enter the torque and RPM, and our free horsepower calculator uses the formula HP = (Torque ร RPM) รท 5252 to give you the answer
Modify the values and click the calculate button to use
By definition
Power = force ร distance / time
Horsepower is a unit of power. It measures how fast work gets done. Think of it this way: torque is how hard you can push something, and horsepower is how fast you can push it.
James Watt came up with the term back in the 1700s. He wanted to sell his steam engines to people who used horses. So he figured out how much work one horse could do in a minute. The number he got? 33,000 foot-pounds per minute. That's one horsepower.
Pretty clever marketing, right? The name stuck, and we still use it today.
550 ft-lbs/second โ 745.7 watts. The original definition by James Watt in 1782.
75 kgf-m/second โ 735.5 watts. Used mainly in Europe.
Exactly 746 watts. Used for electrical machines.
34.5 lbs water evaporated/hour at 212ยฐF โ 9,809.5 watts. Used for steam boilers.
Power at the crankshaft. What manufacturers advertise. Measured with a brake dyno.
European standard. 1 PS โ 0.986 HP. 100 PS โ 98.6 HP. Close enough for most purposes.
For electric motors. 1 HP = 746 watts. Electric motors are more efficient per unit of power.
Power reaching your tires. Always lower than bhp due to drivetrain friction (15-20% loss).
Horsepower = (Torque ร RPM) รท 5252
Looks simple, right? But where does that 5252 come from? It's just a conversion constant โ 33,000 divided by 2ฯ (about 6.2832) gives you roughly 5252. Every time you use this formula, you're asking: "How much work is my engine doing per minute?"
250 lb-ft at 4,000 RPM
HP = (250 ร 4,000) รท 5252 = 190.4 HP
200 lb-ft at 6,500 RPM
HP = (200 ร 6,500) รท 5252 = 247.5 HP
See how the same torque at higher RPM gives more horsepower? That's why high-revving engines make big power.
If you look at a dyno graph, torque and horsepower curves always cross at exactly 5,252 RPM. Why?
HP = (Torque ร 5,252) รท 5,252 โ HP = Torque
The 5,252 cancels out. At that RPM, HP equals torque. Below 5,252 = torque higher. Above 5,252 = HP higher. This is true for every engine, every time.
Using the Wrong Units
Our calculator expects torque in pound-feet (lb-ft). If you enter Newton-meters (Nm), you'll get a wrong answer. Convert: Nm รท 1.356 = lb-ft.
Using Peak Torque and Peak RPM from Different Points
You can't take peak torque from one RPM and multiply by peak RPM from another. Use the torque value at the specific RPM you're calculating.
Forgetting It's a Snapshot
The formula gives HP at one specific RPM โ not peak power. Calculate at multiple RPM points to find the true peak.
Confusing Crank HP with Wheel HP
Manufacturers advertise crank HP. Your wheels see 15-20% less due to drivetrain loss. 300 HP at crank โ 240-255 HP at wheels.
Modifying your car? Calculate before and after to see if those new parts actually added power.
A big drop in calculated horsepower can signal engine problems before you even open the hood.
Boats need enough HP to get on plane. Too little = plowing. Too much = wasted fuel.
Tractors need specific HP for different implements. Knowing your power helps choose the right equipment.
Physics and engineering students use HP calculations as real-world examples of work and power.
Horsepower alone doesn't tell you how fast a car is โ weight matters too. A 300 HP car weighing 3,000 lbs is much faster than a 300 HP car weighing 5,000 lbs.
Power-to-Weight = Horsepower รท Weight (lbs)
3,500 lbs + 350 HP
0.10 HP/lb
2,500 lbs + 250 HP
0.10 HP/lb
They'll accelerate similarly, even though one has 100 more HP. That's why power-to-weight ratio matters more than raw numbers.
Enter your engine's torque in pound-feet (lb-ft)
Enter the RPM where that torque happens
Hit calculate โ the math is done for you instantly
Owner's Manual: Lists peak torque and its RPM โ at the crank, not wheels.
Dyno Run: Chassis dyno measures power at wheels across the full RPM range. Most accurate.
Online Specs: Edmunds, Car and Driver, manufacturer sites list engine specs.
OBD2 Scanner: Cheap scanner + phone app gives live torque and RPM data from your car's computer.
Use torque at the exact RPM you're testing
Make sure torque is in lb-ft, not Nm
Test at multiple RPM points to find peak power
Remember drivetrain loss is about 15-20% for most cars
For electric motors, use the electrical HP formula (1 HP = 746 watts)
You're Using Peak Torque at the Wrong RPM
If your engine makes peak torque at 3,000 RPM but you're calculating at 6,000, you're using the wrong torque value.
Your Torque Number Is from the Crank
Manufacturer specs are at the crank. If measuring at wheels, expect lower numbers.
You're Confusing Units
Double-check you're using lb-ft, not Nm or ft-lb โ they're different.
Your Engine Isn't Stock
Modified engines make different power. Changed intake, exhaust, or tune? Factory specs won't apply.
James Watt figured out that one horse could lift 33,000 pounds one foot in one minute. That's the definition we still use today.
Fun fact: Watt actually overestimated how much work a horse could do. Real horses can only sustain about 0.7-0.8 HP for long periods. But his number worked for marketing, and it stuck.
So when you see a 200 HP car, you're looking at the equivalent of about 250-285 real horses working together. Pretty wild, right?
Electric motors make peak torque from 0 RPM, so the horsepower curve looks different. But the formula is the same โ torque ร RPM รท 5252. The difference is electric motors can maintain peak power over a wider RPM range, which is why they feel so quick off the line.
For electric motors, power is often listed in kilowatts (kW). 1 kW = 1.341 HP. So a 100 kW motor makes about 134 HP.
Use the formula: HP = (Torque ร RPM) รท 5252. Enter torque in pound-feet and RPM into our calculator. Just make sure you're using the right units.
Manufacturers advertise crank horsepower. Your calculation might use wheel torque (15-20% lower). Also, specs show peak HP at a specific RPM โ your calculation might be at a different RPM.
It's a conversion constant. 33,000 (foot-pounds per minute per HP) รท 2ฯ (radians per revolution) โ 5252. It converts rotational force into linear power.
Depends on your goal. High torque = better towing and off-the-line acceleration. High HP = better top speed and passing power. Ideally, you want both. For daily driving, torque feels more useful.
Multiply kilowatts by 1.341. So 100 kW ร 1.341 = 134.1 HP. For electrical motors, 1 HP = exactly 746 watts = 0.746 kW.
Diesels make peak torque at low RPM but can't rev as high as gas engines. Since HP = torque ร RPM รท 5252, lower RPM means lower HP even with high torque.
Under 0.05 HP/lb = economy car. 0.05-0.08 = sporty. 0.08-0.10 = fast. Over 0.10 = supercar territory. A 3,000 lb car with 300 HP = 0.10 HP/lb.
Roughly, but it's not precise. Weight, gearing, traction, and aerodynamics all affect 0-60. A horsepower calculator using torque and RPM is much more accurate.