The formula
In imperial units:
hp = torque (lb-ft) × rpm ÷ 5,252
In metric units the same relationship reads:
kW = torque (N·m) × rpm ÷ 9,549
Neither constant is arbitrary. Power is force × distance ÷ time; a shaft turning at n rpm carries its torque through 2π radians per revolution, so power = 2π × T × n. James Watt defined one horsepower as 33,000 ft·lb per minute, and 33,000 ÷ 2π = 5,252.11. The metric constant is the same derivation in SI: 60,000 ÷ 2π = 9,549.3, with the 60,000 converting minutes to seconds and watts to kilowatts.
Why every dyno chart crosses at 5,252 rpm
Because at exactly 5,252 rpm the equation becomes hp = lb-ft × 1. The two curves are plotted on the same axis, and at that one engine speed the numbers are equal — so they must intersect there, on every chart, for every engine ever built. Below 5,252 rpm the torque line is above the power line; above it, power is above torque.
This is a fact about the units, not about the engine. It is also the quickest way to spot a doctored dyno graph: if the two curves cross anywhere other than 5,252 rpm, either the axes are independently scaled — which is legitimate and common — or the plot is not showing what it claims to. A chart in N·m and kW crosses at 9,549 rpm instead, which most engines never see, so metric plots simply never cross.
Torque is what you feel — power is what gets you there
The everyday version of this argument is wrong in a specific way. What accelerates a car is torque at the wheels, and wheel torque is engine torque multiplied by the gear ratio and the final drive. First gear in a typical hatchback multiplies engine torque by roughly 3.5, then the final drive multiplies it again by around 4 — so a modest 200 N·m engine puts something close to 2,800 N·m through the driveshafts.
That multiplication is why a high-revving engine with unremarkable torque can out-accelerate a torquey one: it can use a shorter gear for the same road speed. Power already contains both halves of the trade — torque and the rpm it is available at — which is why it, not torque, is what predicts a quarter-mile time or a top speed. Change the gearing and the torque at the wheels changes completely; the power does not.
Where torque genuinely matters on its own is what the parts have to survive. Clutch capacity, driveshaft twist and gear-tooth load all care about torque, not power, which is why a 400 N·m diesel can destroy a gearbox that lives happily behind a 400 hp petrol engine.
Crank, wheel and which number you are holding
A manufacturer's figure is measured at the crankshaft on an engine dyno. A rolling road measures at the tyres and reports wheel horsepower, typically 10–15% lower on a manual rear-drive car and more through an automatic or all-wheel drive. Neither is dishonest, but they are not interchangeable, and a "flywheel" figure from a rolling road is a wheel figure with an assumed loss added back on.
Dyno figures also depend on the weather, which is why SAE J1349 correction exists. If you are comparing two runs, compare corrected numbers taken on the same dyno, or compare something the weather cannot argue with — like trap speed.
One point is not a curve
This calculator converts a single operating point. An engine's character lives in the shape of the curve: where torque comes in, how flat it stays, and how far past the torque peak the power keeps climbing. Two engines that both make 295 lb-ft at 6,500 rpm can feel completely different if one of them made 280 lb-ft from 2,000 rpm and the other made 150 lb-ft until 5,000.
Peak power is also almost never at the torque peak. Power keeps rising past the torque peak for as long as torque falls more slowly than rpm rises — that gap between the two peaks is the usable part of the rev range, and it is the part a cam change moves.
Worked examples
- 295 lb-ft at 6,500 rpm → 295 × 6,500 ÷ 5,252 = 365.1 hp (272.2 kW, 370.2 PS).
- 400 N·m at 3,000 rpm → 400 × 3,000 ÷ 9,549 = 125.7 kW, which is 168.5 hp. The same engine at 6,000 rpm on the same torque would make twice that.
- A 250 hp target at 5,000 rpm needs 250 × 5,252 ÷ 5,000 = 262.6 lb-ft, or 356 N·m.
Horsepower by torque and rpm
Every figure below is produced by driving the calculator above at build time, so the chart and the tool cannot drift apart.
Horsepower by torque and rpm
Find your torque figure down the left and the rpm it was made at along the top. The 5,252 column is the one where the horsepower and pound-feet numbers match exactly.
| Torque | 2,000 rpm | 3,000 rpm | 4,000 rpm | 5,252 rpm | 6,000 rpm | 7,000 rpm | 8,000 rpm |
|---|---|---|---|---|---|---|---|
| 100 lb-ft 136 N·m | 38.1 | 57.1 | 76.2 | 100.0 | 114.2 | 133.3 | 152.3 |
| 150 lb-ft 203 N·m | 57.1 | 85.7 | 114.2 | 150.0 | 171.4 | 199.9 | 228.5 |
| 200 lb-ft 271 N·m | 76.2 | 114.2 | 152.3 | 200.0 | 228.5 | 266.6 | 304.6 |
| 250 lb-ft 339 N·m | 95.2 | 142.8 | 190.4 | 250.0 | 285.6 | 333.2 | 380.8 |
| 300 lb-ft 407 N·m | 114.2 | 171.4 | 228.5 | 300.0 | 342.7 | 399.8 | 457.0 |
| 350 lb-ft 475 N·m | 133.3 | 199.9 | 266.6 | 350.0 | 399.8 | 466.5 | 533.1 |
| 400 lb-ft 542 N·m | 152.3 | 228.5 | 304.6 | 400.0 | 457.0 | 533.1 | 609.3 |
| 450 lb-ft 610 N·m | 171.4 | 257.0 | 342.7 | 450.0 | 514.1 | 599.8 | 685.4 |
| 500 lb-ft 678 N·m | 190.4 | 285.6 | 380.8 | 500.0 | 571.2 | 666.4 | 761.6 |
| 600 lb-ft 813 N·m | 228.5 | 342.7 | 457.0 | 600.0 | 685.4 | 799.7 | 913.9 |
The same chart from a newton-metre figure
European figures are quoted in N·m, so here is the same grid entered that way. The horsepower columns are unchanged — only the label on the left differs.
| Torque | 2,000 rpm | 3,000 rpm | 4,000 rpm | 5,252 rpm | 6,000 rpm | 7,000 rpm | 8,000 rpm |
|---|---|---|---|---|---|---|---|
| 100 N·m 74 lb-ft | 28.1 | 42.1 | 56.2 | 73.8 | 84.3 | 98.3 | 112.3 |
| 150 N·m 111 lb-ft | 42.1 | 63.2 | 84.3 | 110.6 | 126.4 | 147.5 | 168.5 |
| 200 N·m 148 lb-ft | 56.2 | 84.3 | 112.3 | 147.5 | 168.5 | 196.6 | 224.7 |
| 250 N·m 184 lb-ft | 70.2 | 105.3 | 140.4 | 184.4 | 210.6 | 245.8 | 280.9 |
| 300 N·m 221 lb-ft | 84.3 | 126.4 | 168.5 | 221.3 | 252.8 | 294.9 | 337.0 |
| 350 N·m 258 lb-ft | 98.3 | 147.5 | 196.6 | 258.1 | 294.9 | 344.1 | 393.2 |
| 400 N·m 295 lb-ft | 112.3 | 168.5 | 224.7 | 295.0 | 337.0 | 393.2 | 449.4 |
| 500 N·m 369 lb-ft | 140.4 | 210.6 | 280.9 | 368.8 | 421.3 | 491.5 | 561.7 |
| 600 N·m 443 lb-ft | 168.5 | 252.8 | 337.0 | 442.5 | 505.6 | 589.8 | 674.1 |
| 700 N·m 516 lb-ft | 196.6 | 294.9 | 393.2 | 516.3 | 589.8 | 688.1 | 786.4 |
FAQ
How do I convert torque to horsepower?
Multiply torque in pound-feet by rpm and divide by 5,252. In metric units, multiply newton-metres by rpm and divide by 9,549 to get kilowatts. Torque alone cannot be converted — you need the engine speed it was measured at.
Why is 5252 the magic number?
One horsepower is 33,000 foot-pounds per minute, and a rotating shaft covers 2 pi radians per revolution. 33,000 divided by 2 pi is 5,252.11, so that is the rpm at which the horsepower and pound-feet numbers are equal.
Is more torque or more horsepower better?
For acceleration, power — because gearing converts engine torque into wheel torque, and power already accounts for both the torque and the rpm it is available at. Torque matters on its own for what the drivetrain must survive: clutches, driveshafts and gear teeth are sized by torque, not power.
Why do the torque and power curves cross on a dyno graph?
Because both are plotted on one axis and they are numerically equal at 5,252 rpm. If a graph is in newton-metres and kilowatts the crossing point moves to 9,549 rpm, which is beyond almost every engine, so metric charts usually never cross.
Does this give crank or wheel horsepower?
Whatever your torque figure was measured at. A crank torque number gives crank power; a wheel torque number from a rolling road gives wheel power. Expect a 10-15% difference between them on a manual rear-drive car, and more through an automatic or all-wheel drive.