In alternators, the ratio of the vector sum of the induced EMFs per coil to the arithmetic sum of the induced EMFs per coil is defined as:

Pitch Factor or Coil Span Factor is defined as the ratio of emf generated in short pitch coil to the emf generated in full pitch coil. It is denoted by Kp and its value is always less than unity.

It can also be defined as the ratio of the vector sum of induced emf per coil to the arithmetic sum of induced emf per coil.

If α be the angle in electrical degrees, by which the span of the coil is less than a pole pitch in the alternator, then mathematically pitch factor is defined as

\({K_p} = \frac{{resultant\;emf\;of\;short\;pitch\;coil}}{{resultant\;emf\;of\;full\;pitch\;coil}} = cos\frac{\alpha }{2}\;\)