Barlow's formula (called "Kesselformel" in German) relates the internal pressure that a pipe can withstand to its dimensions and the strength of its material.
This approximate formula is named after Peter Barlow, an English mathematician.
where
:  : internal pressure,
: : allowable stress,
:   : wall thickness,
: : outside diameter.
This formula (DIN 2413) figures prominently in the design of autoclaves and other pressure vessels.