Let’s consider 5 popular ways how to calculate car engine power using data such as:
 engine revolutions,
 engine capacity
 torsion torque,
 effective pressure in the combustion chamber,
 fuel consumption,
 injector performance,
 car weight,
 acceleration time to 100 km.
Each of the formulas that will be used to calculate a car engine power is quite relative and cannot determine the real horsepower of a car with 100% accuracy. But by making calculations using each of the above garage options, based on one or another indicators, it is possible to calculate at least average value with a 10% error, whether it is a standard or customized engine.
Power is the energy produced by the engine, it is converted into the engine output torque. This is not a constant value. Rotations at which the maximum power can be reached are always indicated next to the maximum power values. The maximum point is reached at the highest average effective pressure in the cylinder (depending on the quality of the fresh fuel mixture, combustion efficiency and heat loss). Modern engines produce the maximum power at the average of 5500–6500 rpm. In the automotive field, it is accepted to measure engine power in horsepower. Therefore, since most of the results are output in kilowatts, you will need a kW to hp conversion calculator.
How to calculate power through torsion torque
The simplest way to calculate a car engine power is by the dependence of torque and revolutions.
Torsion torque
The force multiplied by the arm of its application, which can be produced by the engine to overcome resistance to motion. It determines how fast the engine reaches the maximum power. Calculation torque formula based on the engine capacity is as follows:
Мtorque = VHхPE/0,12566, where
 VH – engine capacity (l),
 PE – average effective chamber pressure (bar).
Engine revolutions
The rotational speed of the crankshaft.
Formula for calculating the explosion engine power is as follows:
P = Mtorque * n/9549 [kW], where:
 Mtorque – engine torsion torque (Nm),
 n – crankshaft revolutions (rpm),
 9549 – the coefficient to enter rotations in rotations per minute, and not in power factors.
Since the result is obtained in kW by the formula, if necessary, you can convert it to horsepower or multiply it by the coefficient of 1.36.
Using these formulas is the easiest way to convert torque to power.
And in order not to go into all the details, a quick calculation of the explosion engine power can be made using our online calculator.
But, unfortunately, this formula reflects only effective power of the engine which does not reach the car wheels fully. After all, there are losses in the transmission, transfer gear, parasitic consumers (air conditioner, generator, HPS, etc.) and it does not take into account such forces as rolling resistance, grade resistance, aerodynamic resistance.
How to calculate power using engine capacity
If you do not know the torque of your car engine, you can also use the following formula to determine its power in kilowatts:
Ne = Vh * pe * n/120 (kW), where:
 Vh — engine capacity, cm³
 n — rotational speed, rpm
 pe — average effective pressure, MPa (at standard petrol engine it is 0.82 — 0.85 MPa, at higherpowered engine — 0,9 МPа, at diesel engine it is from 0.9 to 2.5 МPа correspondingly).
To get the power of the engine in the horsepower, but not in kilowatts, the result should be divided by 0.735.
How to calculate power using air consumption
The same approximate calculation of engine power can be performed based on air consumption. This way of calculation is available to those who have an onboard computer, since it is necessary to fix the consumption rate when the car engine rotates at up to 5.5 thousand revolutions in third gear. The resulting value with mass airflow sensor should be divided by 3 and we obtain the result.
The formula for calculating the explosion engine power based on air consumption is as follows:
Gв [kg]/3=P[hp]
Such a calculation, like the previous one, shows the engine gross power (engine rig test without including losses), which is 10–20% higher than the actual one. And it is worth considering that the readings of the mass airflow sensor are highly dependent on its contamination and calibrations.
How to calculate power using weight and acceleration to 100 km
Another interesting way to calculate engine power on any type of fuel, whether it be petrol, diesel or gas, based on acceleration dynamics. To do this, the car weight (including the driver) and the acceleration time to 100 km are used. And in order for the Power Calculation Formula to be as close to the truth as possible, it is also necessary to take into account the slip losses depending on the type of drive and the speed of reaction of different gearboxes. Approximate losses at start for frontwheel drive is 0.5 seconds and for rear wheel drive is 0.30.4 seconds.
Using this engine power calculator, which helps you to determine engine power based on acceleration dynamics and weight, you can calculate the power of your car quickly and accurately without considering the technical characteristics.
How to calculate power using injector performance
Injector performance is no less effective indicator of a car engine power. Previously, we have considered its calculation and interrelation, therefore, it is easy to calculate the amount of horsepower using the formula. The calculation of the estimated power is performed according to the following scheme:
Where, the workload factor is not more than 7580% (0.75...0.8) the fuel mixture at maximum performance is about 12.5 (enriched), and the BSFC ratio depends on whether you have an, atmospheric or turbocharged engine (atmospheric — 0.40.52, turbocharged — 0.60.75).
When you have found out all the necessary data, enter the values into the corresponding fields of the calculator, press the “Calculate” button and you’ll immediately obtain the result that shows the actual engine power of your car with a slight error. Note that it is not necessary for you to know all the above mentioned parameters; you can calculate the explosion engine power using only one method.
The functional value of this calculator is not in the calculation of the power of a standard car, but in the calculation of a customized car, the weight and power of which have been changed.
FAQ
How can I calculate the power of an internal combustion engine?
Engine power in kW can be calculated from engine displacement and crankshaft rpm. The formula for calculating the power of an engine is as follows:Ne = Vh * Pe * n / 120 (kW), where:
Vh — engine volume, cm³
n — number of crankshaft revolutions per minute
Pe — mean effective pressure, MPa
What factor should be taken into account when calculating the power of the engine?
The power factor (cosϕ) for electric motor power calculation is taken as 0,8 for small engines (less than 5,5 kW) or 0,9 for engines with power over 15 kW.

How to calculate the motor output from the torque?
To determine the power of the engine in kilowatts, when the torque is known, you can use a formula of this kind: P = Mkr * n/9549, where:
Mcr — torque (Nm),
n — crankshaft revolutions (rpm),
9549 is the coefficient to convert revolutions to rpm. 
How to calculate the engine power according to the air consumption?
It is possible to calculate the engine power in kW knowing its air consumption (if you have an onboard computer) using a simple scheme. It is necessary to accelerate the engine in the third gear up to 5500 rpm (torque peak) and according to readings, at that moment, fix the air consumption, and then divide that value by three. As a result of such a mathematical calculation, you can find out the approximate power of the engine with a small error.