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Engine Torque, Displacement & BMEP

Calculate brake mean effective pressure from torque, total swept displacement and crankshaft revolutions per cycle.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

A four-stroke engine producing 100 N·m with total displacement 2,000 cm³ has BMEP 200π kPa, approximately 628.32 kPa or 6.2832 bar.

BMEP = 2π × crank revolutions per cycle × torque / total swept displacement

Worked example

Enter these known values and leave the other values blank.

Engine cycle
Four-stroke engine
Total swept engine displacement
2000 cc
Brake torque
100 N·m
Crank revolutions per cycle
2 rev/cycle
Brake mean effective pressure
628.3 kPa

Assumptions and limitations

  • Displacement, torque, revolutions per cycle and BMEP are positive. Use total swept displacement over all cylinders, not combustion-chamber volume or one-cylinder displacement.
  • The four-stroke preset uses two crankshaft revolutions per cycle; the two-stroke preset uses one. Choose the custom option to supply another positive cycle count.
  • BMEP expresses brake work per cycle divided by displacement. It is an equivalent average pressure, not peak cylinder pressure or a pressure measured throughout the combustion cycle.

Common questions

Why do four-stroke and two-stroke presets differ?

They complete a cycle in different numbers of crank revolutions. At equal torque and displacement, the four-stroke BMEP is twice the two-stroke value.

Do I need RPM for this formula?

No. RPM is needed to relate torque to power, but it cancels when BMEP is calculated directly from torque and displacement.

References

The US fluid ounce uses one 128th of the exact US liquid gallon, replacing the rounded captured reciprocal factor. Kilogram-force centimeters use standard gravity and exactly one centimeter. Pound-force feet use the exact international pound and foot with standard gravity. Pound-force inches use the exact international pound and inch with standard gravity. Pounds-force per square inch use the exact international pound and inch with standard gravity, replacing the rounded captured factor. Pounds-force per square foot use the exact international pound and foot with standard gravity.

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