**First stage ratio**

$$ i_{gr1} = {z_2 \over z_1} $$

This calculation calculates the gear ration of two gear wheels using the number of teeth.

- z1 - number of theeth of first gear
- z2 - number of teeth of the second gear

This calculation is for 3 stage gearbox:

- i_{gr1} - first stage reduction
- i_{gr2} - second stage reduction
- i_{gr3} - third stage reduction

**Three stage gearbox ratio**

$$ i_{gb3} = {i_{gr1} . i_{gr2} . i_{gr3}} $$