ISO 286 Limits & Fits Calculator

Enter a nominal size and an ISO fit — get the hole and shaft limits and the clearance or interference instantly.

Enter a nominal diameter and pick an ISO 286 fit or a single tolerance class. Limits, clearance/interference and fit type compute instantly in your browser.

Nominal size mm · 0–500

Enter a size between 0 and 500 mm.

Fit / tolerance class

Hole-basis: the hole is the H datum (lower limit = nominal) and the shaft letter sets the fit. Size band per ISO 286-1 is "over A, up to and including B".

How fits work

An ISO 286 fit pairs a hole tolerance and a shaft tolerance on the same nominal size. The letter (H, g, p, …) sets the fundamental deviation — where the tolerance zone sits relative to the nominal line — and the number (IT grade, e.g. 6 or 7) sets the width of the zone. Smaller grade = tighter tolerance.

In the hole-basis system (the H fits above), the hole is held constant at H (its lower limit equals the nominal size, EI = 0) and you change the shaft to get the fit you want — this minimises the number of reamers/gauges needed.

Clearance fit: the shaft is always smaller than the hole — there is guaranteed gap (minimum clearance ≥ 0); parts slide or rotate. Interference fit: the shaft is always larger than the hole (maximum clearance < 0); parts are pressed or shrunk together and stay fixed. Transition fit: the zones overlap, so the assembly may end up with a small clearance or a small interference depending on the actual machined sizes — used for accurate location.

ISO fits — FAQ

What do H7 and g6 actually mean?

The letter is the fundamental deviation (zone position) and the number is the IT tolerance grade (zone width). H7 is a hole whose lower limit is exactly the nominal size with an IT7-wide zone going positive. g6 is a shaft sitting just below nominal with an IT6-wide zone. Capital letters denote holes, lowercase letters denote shafts.

What is the difference between clearance, transition and interference?

It comes down to the sign of the gap. Clearance = the shaft is always smaller, so minimum clearance is positive (free movement). Interference = the shaft is always larger, so even the maximum "clearance" is negative (press/shrink fit). Transition = the tolerance zones overlap, so depending on the actual sizes you may get a slight clearance or a slight interference — good for precise location with easy assembly.

Why use hole-basis instead of shaft-basis?

In hole-basis the hole stays the same (H) and only the shaft changes to vary the fit. Holes are made with fixed tooling (drills, reamers, broaches, gauges) that is expensive to vary, while shaft diameters are easy to turn or grind to size — so holding the hole constant is more economical. Shaft-basis (lowercase h hole datum) is preferred when one shaft, like a cold-drawn bar or bearing journal, mates with several different components.

How accurate are these numbers?

The tool encodes the published ISO 286-1 standard tolerance (IT5–IT11) and fundamental-deviation tables in micrometres, including the finer sub-size-bands the standard uses for letters such as c, r, s and u. Values are exact integers in µm and reproduce textbook examples (e.g. Ø50 H7/g6 → hole +25/0, shaft −9/−25, 9–50 µm clearance). Always confirm against the controlling drawing or current standard for critical fits.

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Computed per ISO 286-1 standard tolerance values for guidance; confirm against the controlling drawing/standard for critical fits. Covers nominal sizes 0–500 mm.