Fit calculator per ISO 286
Calculate limit deviations, clearance and interference for hole and shaft per ISO 286 – for all common tolerance classes from 1 to 500 mm nominal size.
Fit calculator
Hole H7
- Upper deviation
- +21 µm
- Lower deviation
- 0 µm
- Maximum size
- 25.021 mm
- Minimum size
- 25.000 mm
- Tolerance T
- +21 µm
Shaft g6
- Upper deviation
- -7 µm
- Lower deviation
- -20 µm
- Maximum size
- 24.993 mm
- Minimum size
- 24.980 mm
- Tolerance T
- +13 µm
- Maximum clearance
- +41 µm
- Minimum clearance
- +7 µm
- Fit tolerance
- +34 µm
Tolerance intervals relative to the zero line (deviations in µm)
Formulas and fundamentals
ISO 286 defines the tolerance system for linear sizes. From nominal size, fundamental deviation (position of the tolerance interval, letter) and tolerance grade (size of the tolerance interval, IT number) the limit deviations of hole and shaft are derived.
Maximum clearance is the difference between the upper deviation of the hole and the lower deviation of the shaft; minimum clearance is the difference between the lower deviation of the hole and the upper deviation of the shaft. Depending on the sign, the result is a clearance fit, transition fit or interference fit.
The calculator uses the published table values of ISO 286-1 (standard tolerances IT5 to IT13, fundamental deviations) for nominal sizes from 1 to 500 mm.
Worked example
For the fit H7/g6 at a nominal size of 40 mm the calculator returns: hole +25/0 µm, shaft -9/-25 µm, maximum clearance 50 µm, minimum clearance 9 µm – a clearance fit as typically used for sliding guides and bearing seats.
Frequently asked questions
What does H7/g6 mean?
H7 describes the tolerance class of the hole, g6 that of the shaft. The letter defines the position of the tolerance interval relative to the zero line, the number the tolerance grade and thus the size of the tolerance interval.
What is the difference between the hole-basis and shaft-basis system?
In the hole-basis system the hole is always made with fundamental deviation H and the fit is adjusted via the shaft tolerance. In the shaft-basis system the shaft is always h and the hole varies. Hole basis is the standard choice because hole-making tools such as reamers are more expensive than turning or grinding a shaft to size.
What does the IT grade express?
The IT grade (e.g. 7 in H7) defines the size of the standard tolerance. The smaller the number, the tighter the tolerance: IT5 to IT7 are used for high-quality mating surfaces, IT8 to IT11 for general manufacturing, IT12 and above for coarse dimensions. The standard tolerance also grows with the nominal size.
When is a fit a clearance, transition or interference fit?
A clearance fit always has clearance in the joined state (minimum clearance greater than or equal to zero), an interference fit always has interference (maximum clearance less than or equal to zero). A transition fit can result in either clearance or interference depending on the actual sizes.
Why is H7/g6 a standard fit?
H7/g6 gives a close clearance fit with small but reliable clearance. Parts can still be assembled by hand and move against each other without noticeable play – ideal for guides, locating features and lightly loaded bearing seats. It also follows the hole-basis system with economically producible tolerance grades.
How does temperature influence fits?
The deviations of ISO 286 apply at the reference temperature of 20 °C. Different operating temperatures or materials with different expansion coefficients change the effective clearance in service. Interference fits are deliberately joined thermally: heating the hub or chilling the shaft temporarily removes the interference during assembly.
Where do the tolerance values come from?
The limit deviations are calculated from the published table values of ISO 286-1 (standard tolerances and fundamental deviations) and cover nominal sizes from 1 to 500 mm.