Enter the number of cylinders, the indicated mean effective pressure (IMEP), engine speed (RPM), piston area (per cylinder), and the stroke length into the calculator (and select whether the engine is 2-stroke or 4-stroke) to determine the Indicated Power. 

Indicated Power Calculator

Enter any 5 values to calculate the missing variable

Indicated Power Formula

Indicated power is the power developed inside an engine’s cylinders by the working gas acting on the pistons. It represents cylinder power before mechanical friction, pumping losses, and accessory losses reduce the usable shaft output.

IP = \frac{100 \, k \, p \, L \, A \, n}{60 \, s}
Symbol Meaning Common Units
IP Indicated power kW
k Number of cylinders count
p Indicated mean effective pressure (IMEP) bar, psi, kPa
L Stroke length m, cm, in, ft
A Piston area per cylinder m², cm², in², ft²
n Engine speed RPM
s Cycle factor 2 for 4-stroke, 1 for 2-stroke

In this form of the equation, pressure is in bar and the result is in kilowatts. The cycle factor accounts for how often each cylinder delivers a power stroke.

Useful Equivalent Forms

If piston area is not already known, compute it from bore diameter first.

A = \frac{\pi D^2}{4}

Displacement per cylinder is the piston area multiplied by the stroke length.

V_d = A \, L

That lets you write the same relationship in terms of displacement per cylinder.

IP = \frac{100 \, k \, p \, V_d \, n}{60 \, s}

If pressure is entered in pascals instead of bar, the kilowatt form becomes:

IP = \frac{k \, p \, L \, A \, n}{60{,}000 \, s}

How to Calculate Indicated Power

  1. Determine the number of cylinders.
  2. Measure or estimate the indicated mean effective pressure.
  3. Enter the stroke length.
  4. Enter the piston area for one cylinder only.
  5. Enter engine speed in RPM.
  6. Select the proper engine cycle: 4-stroke or 2-stroke.
  7. Substitute the values into the formula to find indicated power.

Indicated power scales directly with cylinder count, IMEP, piston area, stroke, and speed.

IP \propto k \, p \, A \, L \, n

Example

For a 4-cylinder, 4-stroke engine with an IMEP of 9 bar, a stroke length of 0.086 m, a bore of 0.082 m, and a speed of 3000 RPM:

A = \frac{\pi (0.082)^2}{4} = 0.00528 \text{ m}^2
IP = \frac{100 \cdot 4 \cdot 9 \cdot 0.086 \cdot 0.00528 \cdot 3000}{60 \cdot 2} \approx 40.9 \text{ kW}

The engine develops about 40.9 kW of indicated power under those operating conditions.

Rearranged Forms for a Missing Input

If you know the target indicated power and need to solve for a different variable, these rearrangements are helpful:

p = \frac{60 \, s \, IP}{100 \, k \, L \, A \, n}
n = \frac{60 \, s \, IP}{100 \, k \, p \, L \, A}
A = \frac{60 \, s \, IP}{100 \, k \, p \, L \, n}
L = \frac{60 \, s \, IP}{100 \, k \, p \, A \, n}

Indicated Power vs. Brake Power

Indicated power is created in the cylinders, while brake power is the power actually available at the crankshaft or output shaft. The difference between them is friction power.

FP = IP - BP
\eta_m = \frac{BP}{IP}

Where:

  • FP = friction power
  • BP = brake power
  • ηm = mechanical efficiency

Practical Notes

  • Use area per cylinder: do not multiply piston area by the number of cylinders before entering it.
  • IMEP is an average pressure: it is not the same as peak cylinder pressure.
  • Use stroke, not rod length: the stroke is the piston’s full travel from top dead center to bottom dead center.
  • Cycle selection matters: a 4-stroke engine produces one power stroke every two revolutions, while a 2-stroke produces one every revolution.
  • Keep units consistent: if one input is converted, all related dimensions should stay in matching unit systems.

Common Input Mistakes

  • Entering total engine displacement in the piston area field.
  • Using bore radius instead of bore diameter when calculating area.
  • Forgetting to switch the cycle factor when changing from 4-stroke to 2-stroke.
  • Mixing pressure units without converting them correctly.
  • Assuming indicated power and brake power are interchangeable.