How to use the fit clearance and interference calculator
A fit is decided entirely by the two tolerance zones you put on the hole and the shaft. The arithmetic is short: maximum clearance = largest hole − smallest shaft and minimum clearance = smallest hole − largest shaft. When the minimum clearance turns negative, its absolute value is the maximum interference.
The result falls into one of three classes. A minimum clearance of zero or more is a clearance fit, a maximum clearance of zero or less is an interference fit, and opposite signs mean a transition fit that can come out either loose or tight. Worked check: a 1.0000 in hole at +0.0008/0.0000 in with a shaft at −0.0003/−0.0008 in gives 0.0016 in maximum and 0.0003 in minimum clearance.
Pull the deviation numbers straight from your tolerance table rather than estimating them. Inch drawings use the ANSI B4.1 classes (RC running and sliding, LC locational clearance, LT transition, LN locational interference, FN force and shrink), while US metric drawings follow ANSI B4.2, which adopts the ISO 286 system and the familiar H7/g6 symbols. The math here is unit agnostic, so an ISO 286 job can be entered as mm with micrometre deviations and read back in the same units.
Tolerances assume parts at 68 F (20 C), and an interference fit needs more than this clearance check: press force, hoop stress and the assembly method all have to be verified separately.
Frequently asked questions
Yes, on metric drawings. ANSI B4.2 adopts the same preferred metric limits and fits as ISO 286, so H7/g6 means the same thing in the US. Inch drawings instead use the ANSI B4.1 classes such as RC running and sliding, LC locational clearance, LT transition, LN locational interference and FN force or shrink fits.
If maximum clearance is positive but minimum clearance is negative, the assembly is a transition fit: some part pairs will have a gap and others will be tight. It can locate a part accurately but it is not suitable for a rotating joint.