It depends on the driving situation(load, speed, rpm), engine (Gasoline/Diesel,effective compression ratio), torque requirement.

As a rule of thumb for a classical engine.

-around 2 bar at light cruise

-around 4 bar easy acceleration

-around 8 bar hard acceleration

- 8-16 bar full throttle

Thanks William

i agree.

A bit more details :

Naturally aspirated gasoline engine : between 2 bar (low load)  to 10 bar (full load)

Turbocharged gasoline engine : up to 26 bar (Peugeot EP6 1.6L THP 270ch)

Turbocharged Diesel engine : up to 30 bar (Renault R9M engine 1.6L)

You can calculate it from the torque (T) and the engine displacement (D) by the following formula : BMEP (Pa) = 4*pi*T / D (m3)