# Brake Mean Effective Pressure (BMEP) Calculator

URL: https://speedycalculator.com/calculators/physics/brake-mean-effective-pressure-bmep/
Last updated: 2026-10-30

> The BMEP calculator finds an engine's brake mean effective pressure – the average cylinder pressure that would produce its measured torque – from torque, displacement and the number of strokes per cycle.

## Inputs

- Engine type
- Engine displacement (cm³ (cc), L, in³ (CID), m³)
- Torque (N·m, lbf·ft, kgf·m, N·mm)

## Results

- Brake mean effective pressure
- Specific torque

## Formula

```
BMEP = 2π·n_c·T / V_d  (n_c = 2 for four-stroke, 1 for two-stroke)
```

## Explanation

BMEP lets you compare how hard engines of different sizes work. Naturally aspirated petrol engines reach about 10–13 bar; turbocharged ones 20–30 bar; truck diesels around 20+ bar.

### How to use the Brake Mean Effective Pressure

- **Engine type**
- **Engine displacement**
- **Torque**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose the engine cycle, enter the displacement and torque (at the same rpm).

### Inputs explained

FieldWhat to enterEngine typeChoose one: Four-stroke, Two-strokeEngine displacementUnits: cm³ (cc), L, in³ (CID), m³TorqueUnits: N·m, lbf·ft, kgf·m, N·mm

### What each result means

- **Brake mean effective pressure** = 2×pi×[Engine type]×[Torque]÷[Engine displacement]
- **Specific torque** = [Torque]÷([Engine displacement]×1000)

### Example values

How the main result changes when **Engine displacement** changes and everything else stays at the example values above:

Engine displacement (cm³ (cc))Brake mean effective pressure (bar)1,00025.13271,50016.75522,00012.56642,50010.05313,0008.37764,0006.2832

## Worked example

Inputs — Engine type: Four-stroke; Engine displacement: 2,000 cm³ (cc); Torque: 200 N·m.

Results — **Brake mean effective pressure = 12.5664 bar**; Specific torque = 100 N·m/L.

## Key terms

- **Displacement**: Total swept volume of all cylinders.

## FAQ

**What is a good BMEP?**
10–13 bar for naturally aspirated petrol engines; 20+ bar turbocharged.

**Why use BMEP?**
It removes engine size, so efficiency of different engines can be compared.

**Is BMEP a real pressure?**
No – it is a theoretical average over the cycle.

**How does turbocharging raise BMEP?**
More air per cycle allows more fuel and torque.


## Sources

- [OpenStax – University Physics Volume 1](https://openstax.org/details/books/university-physics-volume-1)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)