Press Fit Calculator
Hole and shaft limits, and the resulting clearance or interference, for a nominal diameter and an ISO 286 hole-basis fit.
- Rev
- 2026-08-01
- Formulas
- 2
- Assumptions
- 4
An ISO 286 fit is two tolerance zones: a hole class and a shaft class. In a hole-basis system the hole is fixed at an H class with a lower deviation of zero, and the shaft class is what creates clearance, transition or interference.
Pick the nominal diameter and the fit; the tool reads the tabulated deviations for the size band that diameter falls into and works out both extremes of the assembly. Values come straight from the ISO 286 chart on this site — nothing is interpolated between size bands.
Tabulated from over 0 up to 120 mm.
Hole H7, shaft p6.
- Size band
- over 18 to 30 mm
- Hole H7
- +21 / 0 µm
- Shaft p6
- +35 / +22 µm
Fit range
Interference of 1–35 µm
Max clearance
−1µm
negative = interference
Min clearance
−35µm
negative = interference
Hole H7
25.000 / 25.021mm
min / max
Shaft p6
25.022 / 25.035mm
min / max
Assembly force and hoop stress are not tolerance questions — feed the worst-case interference into a Lamé thick-cylinder calculation before committing.
Substitution
C_max = ES − ei = +21 − (+22) = −1 µm
C_min = EI − es = 0 − (+35) = −35 µm
Assumptions
A number without its assumptions is not citable. These are the conditions the result is valid under.
- Hole-basis system (ISO 286-1). The hole is the fixed member; the shaft class varies the fit.
- Deviations are tabulated per size band — “over 3 up to and including 6 mm” and so on. A diameter is evaluated in the band it falls into; no value is interpolated between bands.
- The tabulated range on this site runs 0–120 mm. Diameters outside it are reported as out of range rather than extrapolated.
- Tolerance limits describe the parts as manufactured at 20 °C. They say nothing about assembly force, hoop stress or the temperature differential needed for a shrink fit — those need the Lamé equations plus the material properties of both parts.
Formulas
What the tool computes, written out. Every symbol is defined.
Maximum clearance
C_max = ES − ei
- ES
- upper deviation of the hole
- EI
- lower deviation of the hole
- es
- upper deviation of the shaft
- ei
- lower deviation of the shaft
Minimum clearance
C_min = EI − es
A negative clearance is an interference of the same magnitude. When C_max and C_min have opposite signs the fit is a transition fit: the assembly may end up either way depending on where the two parts land in their tolerance bands.
Questions
6 questionsWhat is a press fit?
A fit where the shaft is larger than the hole across the whole tolerance range, so assembly requires force or a temperature differential. In ISO 286 terms the minimum and maximum clearance are both negative — H7/s6 and H7/u6 are the classic examples.
What does H7/p6 mean?
The letter gives the position of the tolerance zone relative to the nominal size and the number gives the IT grade — the width of the zone. H is a hole whose lower deviation is zero, 7 is IT7; p is a shaft positioned above the nominal size, 6 is IT6. Capital letters are holes, lower case are shafts.
Why does H7/p6 show clearance at small diameters?
Because the p6 shaft zone only clears the H7 hole zone once the diameter is large enough. Below roughly 25 mm the two zones overlap, which makes H7/p6 a transition fit at those sizes: some assemblies will press, some will slide. That is a property of the standard, not a rounding artefact.
Which fit should I choose?
H7/g6 for a sliding fit that must still locate accurately, H7/h6 for a locational clearance fit assembled by hand, H7/k6 for a locational transition fit that needs light force and a mallet, H7/p6 for a light press fit that can still be dismantled, and H7/s6 where the joint must transmit torque without a key.
How much force does a press fit need?
That is not a tolerance question. Assembly force depends on the interference, the contact area, the elastic moduli and Poisson's ratios of both parts, the hub outside diameter, the surface finish and the coefficient of friction — the Lamé thick-cylinder equations. Use this tool for the interference range, then feed the worst case into a stress calculation.
Do these values change with temperature?
The tabulated deviations are defined at 20 °C. Differential thermal expansion between an aluminum hub and a steel shaft can consume or create tens of microns over a modest temperature swing, which is enough to turn a light press fit into a clearance fit.
Standards and references
- ISO 286-1:2010 — ISO code system for tolerances on linear sizes: basis of tolerances, deviations and fits.
- ISO 286-2 — tables of standard tolerance classes and limit deviations for holes and shafts.