Press Fits - quick calculator

By @GregLocock and @Desertfox

The equations are called Lame’s equations.

Here’s an online calculator:

Under interference fits. You have to log in to be able to change the pin diameter.

Alternatively desertfox looked up the equations, so you can roll your own:

Here are the formulas you need:

       Pa= f*3.142*d*L*Pc
  • f=friction coefficient
  • Pc=contact pressure between the two members
  • d= nominal shaft dia
  • L=length of external member.
  • Pa= axial force required to interference fit

To calculate Pc for a given interference use the formula:


  • x = total interference
  • Dc=dia of shaft
  • Di = inner dia of shaft(this is zero for solid shaft)
  • Do= outside dia of collar
  • Uo=poissons ratio for outer member
  • Ui=poissons ratio for inner member
  • Eo=modulus of elasticity for outer member
  • Ei=modulus of elasticity for inner member

[This formula for Pc will simplify if the materials are the same.]