How to use this calculator
- Enter engine torque. Use brake torque measured at the crankshaft.
- Enter displacement. Use total engine displacement.
- Choose engine cycle. Select four-stroke or two-stroke.
- Read BMEP. Compare BMEP and torque per litre.
How it works
BMEP normalizes torque by displacement. For a four-stroke engine, the calculator uses BMEP = 4 x pi x torque / displacement. For a two-stroke, the cycle factor is 2 x pi.
Use the bore and stroke calculator if you need displacement first, or the engine airflow calculator when airflow sizing is the next question.
Worked example
Verified against the live calculator
A four-stroke 2.0 L engine making 300 N*m has BMEP of about
4 x pi x 300 / 0.002 = 1.88 MPa, or 18.8 bar.
Frequently asked questions
What is BMEP?
Brake mean effective pressure is a normalized torque metric. It is the average effective pressure that would produce the measured brake torque over the engine displacement.
Is BMEP cylinder pressure?
No. BMEP is a torque-normalized average pressure, not peak combustion pressure or measured in-cylinder pressure.
Why does two-stroke vs four-stroke matter?
A four-stroke engine has one power cycle every two crank revolutions, while a two-stroke has one every revolution, so the cycle factor differs.
What is BMEP useful for?
It lets you compare torque output across different engine sizes and layouts.
Method & assumptions
- BMEP is calculated from brake torque and total displacement.
- It is not peak cylinder pressure, knock limit, boost pressure or combustion pressure.