What this power and torque calculator does
This calculator helps you quickly solve the relationship between power, torque, and engine speed (RPM). It is useful for car enthusiasts, motor designers, mechanics, students, and anyone comparing drivetrain performance.
You can calculate any one of these three values when the other two are known:
- Power from torque and RPM
- Torque from power and RPM
- RPM from power and torque
Power vs. torque: the practical difference
Torque
Torque is twisting force. It tells you how strongly a shaft (or crankshaft) is trying to rotate. In vehicles, higher torque generally improves low-speed pulling ability and launch feel.
- SI unit: Newton-meter (N·m)
- Imperial unit: pound-foot (lb-ft)
Power
Power is the rate of doing work. In an engine or motor, power combines how much torque is produced and how fast that torque is applied (RPM). Power is what often correlates with top-end performance.
- SI units: Watts (W), kilowatts (kW)
- Imperial unit: horsepower (hp)
Core equations used
- Power: P = T × 2π × RPM / 60
- Torque: T = P × 60 / (2π × RPM)
- RPM: RPM = P × 60 / (2π × T)
In these equations, power must be in Watts and torque in N·m. This calculator automatically converts your selected units before computing the result.
How to use this calculator
- Select what you want to calculate from the dropdown.
- Enter the two known values.
- Choose the correct units for power and torque.
- Click Calculate to see the answer and unit conversions.
Worked examples
Example 1: Find power from torque and RPM
If torque is 300 N·m at 2500 RPM, power is:
- P = 300 × 2π × 2500 / 60 = 78,540 W
- That equals about 78.54 kW or 105.32 hp
Example 2: Find torque from power and RPM
If power is 120 kW at 4000 RPM:
- T = 120,000 × 60 / (2π × 4000) = 286.48 N·m
- That equals about 211.30 lb-ft
Example 3: Find RPM from power and torque
If power is 75 hp and torque is 150 lb-ft, convert both to SI and solve for RPM:
- 75 hp ≈ 55,927 W
- 150 lb-ft ≈ 203.37 N·m
- RPM = 55,927 × 60 / (2π × 203.37) ≈ 2,627 RPM
Useful conversion constants
- 1 hp = 745.6999 W
- 1 kW = 1000 W
- 1 lb-ft = 1.3558179 N·m
- 1 N·m = 0.7375621 lb-ft
Common mistakes to avoid
- Mixing units without converting (e.g., using hp directly in SI formula).
- Using zero or negative RPM/torque where physical context requires positive values.
- Confusing lb-ft and ft-lb notation in non-engineering discussions.
- Assuming peak torque and peak power happen at the same RPM (they usually do not).
Final note
Power and torque are not competing metrics—they are connected. Torque tells you rotational force; power tells you how fast that force can be delivered. Use both together to better understand engine and motor performance across the rev range.