Method of calculating the thrust forces:

The thrust forces or gas loads can be calculated for the engine, or for any flow section of the engine, provided that the areas, pressures, velocities and mass flow are known for both the inlet and outlet of the particular flow section.
The distribution of thrust forces shown in Fig 2.1. can be calculated by considering each component in turn and applying some simple calculations. The thrust produced by the engine is mainly the product of the mass of air passing through the engine and the velocity increase imparted to it (ie. Newtons Second Law of Motion), however the pressure difference between the inlet to and the outlet from the particular flow section will have an effect on the overall thrust of the engine and must be included in the calculation.
To calculate the resultant thrust for a particular flow section it is necessary to calculate the total thrust at both inlet and outlet, the resultant thrust being the difference between the two values obtained.

Calculation of the thrust is achieved using the following formula:
Thrust = (A*P)+WVj/g
Where

A = Area of flow section in sq. in.
P = Pressure in lb. per sq. in.
W = Mass flow in lb. per sec.
Vj = Velocity of flow in feet per sec.
g = Gravitational constant 32.2 ft. per sec. per sec.