ISO 286 Fit Calculator

What Is a Fit?

A fit describes the dimensional relationship between two mating parts — typically a hole and a shaft — that share the same nominal size but may have tolerance zones that differ in position and width. The permissible limit dimensions are governed by ISO 286-1:2010 and ISO 286-2:2010.

Three Pieces Define Every Fit

• Nominal dimension — the basic diameter of the hole or shaft.
• Tolerance grade (IT) — numbered 01–18. A lower number means a tighter, narrower tolerance band.
• Tolerance position — designated by a letter (A–ZC for holes, a–zc for shafts). The letter sets where the tolerance zone sits relative to the nominal size.

Fit Types

• Clearance fit — the largest shaft is always smaller than the smallest hole, guaranteeing a gap.
• Interference fit (press fit) — the smallest shaft is always larger than the largest hole, requiring force to assemble.
• Transition fit — depending on actual part dimensions, the result can be either a slight clearance or a slight interference.

This calculator determines the upper and lower deviations, maximum and minimum sizes, and centre of tolerance for any combination of nominal dimension and tolerance class. When both a hole and shaft are selected, it also classifies the resulting fit type.