This torque to horsepower calculator converts engine torque (in lb-ft) at a given RPM into horsepower, using the fundamental power equation. It also shows the kilowatt equivalent — handy for comparing a dyno torque figure against an advertised HP number, or converting between US and metric power units.
Torque to HP Formula
This is the fundamental relationship between rotational force (torque), rotational speed (RPM), and power output (HP). The constant 5,252 converts the imperial units into consistent power output. The same relationship in metric is: kW = Nm × RPM / 9,549.
Once you have HP, convert to kilowatts with:
Torque vs Horsepower: What's the Difference?
Torque is the twisting force the engine produces — what you feel as low-end pull. Horsepower is the rate at which that work is done, combining torque with how fast the engine spins. An engine can make big torque at low RPM yet modest horsepower, because power depends on both. This is why diesels feel strong off the line (high torque, lower RPM) while high-revving sport engines make big horsepower from less torque spun faster. Peak HP almost always occurs at higher RPM than peak torque.
The 5252 RPM Crossover
On any dyno graph, the horsepower and torque curves cross at exactly 5,252 RPM. It's not a coincidence — it falls straight out of the formula. Below 5,252 RPM torque is the larger number; above it, horsepower is. The constant itself comes from 33,000 ft-lb/min (the definition of one horsepower) divided by 2π, since there are 2π radians per revolution.
Torque to HP at Common RPM
| Torque (lb-ft) | @ 3,000 RPM | @ 5,252 RPM | @ 7,000 RPM |
|---|---|---|---|
| 200 | 114 HP | 200 HP | 267 HP |
| 300 | 171 HP | 300 HP | 400 HP |
| 450 | 257 HP | 450 HP | 600 HP |
| 600 | 343 HP | 600 HP | 800 HP |
Worked Example
Given: An engine produces 450 lb-ft of torque at 4,500 RPM
Step 1: HP = 450 × 4500 / 5252
Step 2: Numerator = 450 × 4500 = 2,025,000
Step 3: HP = 2,025,000 / 5252 = 385.6 HP
Step 4: kW = 385.6 × 0.7457 = 287.5 kW
This formula calculates power at a specific operating point. Peak HP is achieved where the product of torque × RPM is maximized, not necessarily at peak torque RPM.
Frequently Asked Questions
Multiply torque (lb-ft) by RPM, then divide by 5,252. For example, 400 lb-ft at 4,500 RPM = 400 × 4500 / 5252 = 342.7 HP. If your torque is in Newton-meters, convert first: lb-ft = Nm × 0.7376.
Yes. First calculate power in kW using kW = Nm × RPM / 9,549, then convert to HP: HP = kW × 1.3410. Alternatively, convert Nm to lb-ft (multiply by 0.7376) and use the standard formula. Our Torque to kW calculator handles Nm directly.
Because HP = Torque × RPM / 5252. Even after peak torque, as long as torque doesn't fall fast enough, rising RPM keeps increasing HP. Peak HP occurs at the RPM where Torque × RPM is maximized. Once the engine can no longer maintain torque faster than RPM rises, HP peaks and starts dropping.
Use HP = (torque in lb-ft × RPM) ÷ 5252. You need both the torque figure and the RPM at which it occurs.
No. Horsepower depends on how fast the torque is delivered, so RPM is required. The same torque at higher RPM produces more horsepower.