Horsepower Calculator · Practical guide
Why Torque and Horsepower Cross at 5252 RPM
The crossover is built into the definition of horsepower — here is the math, plus examples above and below 5,252 RPM.
At a glance
The Short Answer
Torque and horsepower curves cross at 5,252 RPM because of how horsepower is defined: HP = Torque x RPM / 5252. At exactly 5,252 RPM the equation becomes HP = Torque x 5,252 / 5,252, so the horsepower number equals the torque number — as long as torque is measured in lb-ft.
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Horsepower Calculator
Enter your own values, then compare the result with the examples below.
Results
What Happens Above and Below 5252
Below 5,252 RPM the torque value is always larger than the horsepower value; above it, horsepower is larger even when torque is falling. That is why torquey diesels post modest horsepower figures, while high-revving engines make big horsepower from small torque.
| Torque (lb-ft) | RPM | Horsepower |
|---|---|---|
| 300 | 3,000 | 171.4 |
| 300 | 4,000 | 228.5 |
| 300 | 5,252 | 300.0 |
| 300 | 6,000 | 342.9 |
| 250 | 7,000 | 333.0 |
Why the Number Is 5252
James Watt defined one horsepower as 33,000 foot-pounds of work per minute. One revolution sweeps 2pi feet at a one-foot radius, so RPM x torque (lb-ft) x 2pi gives foot-pounds per minute, and dividing by 33,000 yields horsepower. Since 33,000 / 2pi = 5,252.1, the crossover point is baked into the definition itself.
In metric units there is no neat crossover at 5252: with torque in Nm, power in kilowatts equals torque x RPM / 9,549, so the curves cross at 9,549 RPM instead.
Frequently Asked Questions
Do the curves always cross at 5252 RPM in every car?
Yes, whenever torque is plotted in lb-ft and horsepower in hp on the same numeric scale. The crossover is a math artifact, not a tuning target.
Can horsepower keep rising if torque falls?
Yes. As long as RPM rises faster than torque drops, horsepower keeps climbing. That is why peak power sits past the torque peak.
What if my torque is in Nm?
Convert Nm to lb-ft by dividing by 1.3558 first, or compute kilowatts directly with kW = Nm x RPM / 9549.
Is 5252 exact?
33,000 divided by 2pi is 5,252.11, so 5252 is a rounding. The calculator uses 5252, matching standard dyno math.