Some good pipe fitting formulas are Barlow's formula, geometry formulas and sprinkler system formulas. Additionally, pipe fitting loss calculations with K factors help to determine pressure loss within the fitting with liquid flow at a set velocity.
Pipe fitting formulas help welders and pipe fitters determine how to set a pipe so that it handles fluid flow stress and internal pressure from its walls. Barlow's formula, for example, is used to calculate a pipe's bursting pressure. Also known as the outside diameter formula, it predicts the bursting pressure by multiplying the pipe's wall thickness by 2, multiplying this by the unit stress per square inch and then dividing the answer by the tubing's outer diameter.