BMEP Calculator: BMEP = 4 pi T / Vd

A measure of how hard an engine works, from its torque and size.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose which quantity you want to find.

Enter the other values in the units shown.

The calculator gives the answer with the formula, the substituted numbers, and the answer in other units.

Formulas used

  • BMEP = \frac{4\pi T}{V_d}
  • T = \frac{BMEP\,V_d}{4\pi}

Worked example

With the default numbers in the calculator above:

  1. The formula, arranged to find the brake mean effective pressure: brake mean effective pressure = (4 x pi x torque) / (engine displacement)
  2. Put the values in (every value in its SI unit): brake mean effective pressure = (4 x pi x 200) / (0.002)
  3. The answer: brake mean effective pressure: 1.25664e+6 Pa
  4. The same answer in other units: 1256.64 kPa; 12.5664 bar; 182.26 psi

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What is BMEP?

The average pressure in the cylinders over the whole cycle that would produce the engine's brake torque.

Why compare engines by BMEP?

It removes the effect of engine size, so you can compare the work done per unit of displacement.

What is a typical value?

Naturally aspirated petrol engines are 9 to 12 bar, turbocharged petrol 15 to 25 bar, and diesel 15 to 30 bar.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any internal combustion engine text (mean effective pressure).

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