ISO Fit Calculator

Compare the four standard ISO 286 hole-basis fits — H7/g6, H7/h6, H7/k6, and H7/m6 — for any nominal diameter, side by side.

How to use it

1. Enter the nominal diameter in millimeters — the basic size shared by the hole and shaft before tolerances are applied.
2. That's it. The calculator looks up the ISO 286 fundamental tolerance grade (IT7 for the hole, IT6 for the shaft) and fundamental deviation for each of the four shaft letters at that diameter, then reports all four fits at once.

What "hole-basis" means

In the hole-basis system, the hole is always toleranced as H — its lower deviation is fixed at zero, so the hole's minimum size always equals the nominal diameter. Every fit is then set by which shaft tolerance zone pairs with it:

• H7/g6 and H7/h6 — clearance fits. The shaft is always the same size as or smaller than the hole, so the parts always separate freely. h6/H7 is the tightest clearance fit commonly used (minimum clearance is exactly zero); g6/H7 gives a small guaranteed running clearance.
• H7/k6 and H7/m6 — transition fits. Depending on where the actual (in-tolerance) hole and shaft land, the assembly can come out with a small clearance or a small interference. m6 is the tighter of the two, biased further toward interference.

What you get back

For each of the four fits: the physical size limits of the hole and shaft (in mm), the minimum and maximum fit (in µm — positive is clearance, negative is interference), and an explicit Clearance / Transition / Interference classification. A tolerance-zone diagram plots all five zones (the shared H7 hole, plus all four shafts) on one scale, so you can see at a glance how far each shaft's zone sits from the hole's.

Limits

This covers the four most common preferred hole-basis fits (per ISO 286 / mechanical design references such as Shigley's) across the standard diameter range up to 500 mm. It does not cover every ISO fit class (there are dozens of shaft letters and IT grades in the full standard) or the shaft-basis system. Treat it as a fast comparison for early design selection — check the governing ISO 286 tables for a final production drawing, especially near a diameter-range boundary or outside the common range.

Privacy

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Related tools

For the mechanics of a press/shrink fit once you've picked an interference-class combination, see the Press Fit Interference Calculator. For stacking tolerances across a chain of dimensions, see the Tolerance Stackup Calculator.