Enter the force and mass flow rate into the calculator to determine the specific impulse.

Specific Impulse Formula

The following formula is used to calculate a specific impulse.

Isp = F / (mdot*g)
  • Where Isp is the specific impulse (N/kg*m/s)
  • F is the force (N)
  • mdot is the mass flow rate (kg/s)
  • g is the acceleration due to gravity (m/s^2)

To calculate specific impulse, multiply the mass flow rate by the acceleration due to gravity, then divide the force by that result.

Specific Impulse can also be calculated by dividing the total impulse by the weight.

What is specific impulse?


Specific impulse is defined as the total impulse per unit of weight. This is most often used when looking propulsion systems and fuel within rockets.

How to Calculate Specific Impulse?

Example Problem:

The following example outlines the steps and information needed to calculate a specific impulse.

First, determine the force generated by the system. In this example, the force is measured to be 10,000 N.

Next, determine the mass flow. For this example, the mass flow rate is measured to be 25 kg/s.

Finally, calculate the specific impulse using the information above along with the acceleration due to gravity.

Isp = F / (mdot*g)

Isp = 10,000 / (25*9.81)

Isp = 40.77