Calculators · Engine
Torque, power and BMEP calculator
Torque and power are two views of the same thing: power is torque multiplied by rotational speed. These calculators convert between them at any RPM, and go further with two figures that let you compare engines of very different sizes fairly — brake mean effective pressure (BMEP), which measures how much torque each litre produces, and specific output in kW or hp per litre.
Power from torque and RPM
Converts torque at a given engine speed into power. Use it to check a dyno sheet or to see how much power a torque figure represents at a particular RPM.
P [kW] = T [Nm] × rpm / 9,549.3
Torque from power and RPM
Works out the torque behind a quoted power figure at a given speed. Useful when a specification lists peak power but not the torque at that point.
T [Nm] = P [kW] × 9,549.3 / rpm
Brake mean effective pressure (BMEP)
BMEP is the average cylinder pressure that would produce the measured torque. Because it is independent of engine size, it shows how well an engine uses its displacement — a small turbo engine and a large diesel can be compared directly.
BMEP = (2π × n_R × T) / V_d n_R = 2 for four-stroke, 1 for two-stroke
Specific output per litre
Divides power and torque by displacement. It is the quickest way to see how highly tuned an engine is: naturally aspirated road engines sit far below modern turbo engines.
kW/L = P / (V_d / 1,000) Nm/L = T / (V_d / 1,000)
Worked example: a 2.0-litre turbo engine
- 400 Nm at 4,000 rpm: 400 × 4,000 / 9,549.3 = 167.6 kW (224.7 hp).
- BMEP: 4π × 400 / 0.001998 m³ = 2.52 MPa = 25.2 bar — typical of a modern turbo petrol engine.
- With 200 kW peak power: 200 / 1.998 = 100 kW per litre (134 hp/L).
Typical BMEP and specific output
| Engine type | Peak BMEP | Specific power |
|---|---|---|
| Naturally aspirated petrol | about 10 – 13 bar | about 45 – 80 kW/L |
| Turbocharged petrol | about 18 – 25 bar | about 75 – 120 kW/L |
| Passenger car diesel | about 18 – 24 bar | about 45 – 70 kW/L |
| Heavy-duty truck diesel | about 20 – 27 bar | about 25 – 35 kW/L |
Related
About these results
Results are theoretical estimates from standard engineering formulas. Real-world figures depend on conditions these formulas do not capture. Always follow the manufacturer's specifications for maintenance, loading and safety decisions.
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