What is the tolerance of a 25 mm H6 hole?

A 25 mm H6 hole runs 25.000 to 25.013 mm — deviations of 0 to +13 µm, a tolerance band 13 µm wide.

H6 is an ISO 286 hole tolerance. The H sets the fundamental deviation — zero deviation — the basic hole — and the 6 is the IT6 tolerance grade, which sets how wide the band is. Precision basic hole for close-running and transition fits.

How wide is the IT6 tolerance band?

IT6 is 13 µm wide for nominal sizes over 18 up to 30 mm, and widens with size — the full band table is on this page.

ISO 286 · hole tolerance · IT6

H6 Tolerance — Hole Limits by Nominal Size

https://shopmath.org/fits/h6-hole · data verified August 1, 2026

A 25 mm H6 hole runs 25.000 to 25.013 mm — deviations of 0 to +13 µm on a tolerance band 13 µm wide. The H sets where the band sits (zero deviation — the basic hole) and IT6 sets how wide it is. Precision basic hole for close-running and transition fits. All values apply at 20 °C.

Feature: hole
Letter: H
Grade: IT6
Sizes: 13
Standard: ISO 286-1:2010

H6 hole at Ø25 mm · deviation, µm

+13 / 0

Max Ø: 25.013mm
Min Ø: 25.000mm
Band: 13µm

Deviations from the 25 mm nominal size, at 20 °C. Every other verified size is in the table below.

Source: ISO 286-1:2010, ISO 286-2:2010
Formula: max Ø = nominal + ES min Ø = nominal + EI
Assumptions: Ø25 mm nominal, 18–30 mm size step, plain cylindrical feature, 20 °C. Deviations are tabulated in the standard and compiled here; the limits are those deviations added to the nominal size.
Verified: August 1, 2026

H6 Hole Limits at Every Verified Nominal Size

Deviations in micrometres and finished limits in millimetres. These are the thirteen nominal sizes with verified demand; the deviation pattern continues across the full ISO 286 size range.

H6 hole tolerance — deviations and limits by nominal size
Property	Deviation, µm		Limits, mm		Property
Nominal Ø	Upper	Lower	Min	Max	Tolerance band, µm
5 mm	+8	0	5.000	5.008	8
6 mm	+8	0	6.000	6.008	8
8 mm	+9	0	8.000	8.009	9
10 mm	+9	0	10.000	10.009	9
12 mm	+11	0	12.000	12.011	11
16 mm	+11	0	16.000	16.011	11
20 mm	+13	0	20.000	20.013	13
25 mm	+13	0	25.000	25.013	13
30 mm	+13	0	30.000	30.013	13
40 mm	+16	0	40.000	40.016	16
50 mm	+16	0	50.000	50.016	16
80 mm	+19	0	80.000	80.019	19
100 mm	+22	0	100.000	100.022	22

Deviations are relative to the nominal size: positive is above it, negative below. Limits assume the ISO 286 reference temperature of 20 °C.

The IT6 Tolerance Grade in H6, Across ISO 286 Size Bands

The number in H6 is the IT grade, and it sets how wide the tolerance band is. The band widens with size — that is the whole point of a graded tolerance system.

IT6 standard tolerance by nominal size band
Nominal size band	Tolerance, µm	Tolerance, mm
over 0 to 3 mm	6	0.006
over 3 to 6 mm	8	0.008
over 6 to 10 mm	9	0.009
over 10 to 18 mm	11	0.011
over 18 to 30 mm	13	0.013
over 30 to 50 mm	16	0.016
over 50 to 80 mm	19	0.019
over 80 to 120 mm	22	0.022
over 120 to 180 mm	25	0.025
over 180 to 250 mm	29	0.029
over 250 to 315 mm	32	0.032
over 315 to 400 mm	36	0.036
over 400 to 500 mm	40	0.040

Bands are open at the bottom and closed at the top: 'over 18 to 30 mm' includes 30 mm and excludes 18 mm.

Fundamental Deviation of the H hole Tolerance in H6

The letter in H6 sets where the tolerance band sits relative to the nominal size: zero deviation — the basic hole. The grade then adds the band width to that starting point.

H fundamental deviation

0µm

At every one of the 25 ISO 286 size bands, from 0 to 500 mm.

The H deviation does not change with size — it is the lower limit (ei / EI) for every band, so IT6 alone decides how wide the band is. That is what makes H6 the basic hole: one limit is pinned at the nominal size and the grade opens the other. Sizes are given in the limits table above, and the full band-by-band listing is in this page’s Markdown twin.

Sources and Method for the H6 Tolerance Data

H6 limitscomputed

limits computed from the compiled ISO 286 tables: ISO 286-1 IT grades and ISO 286-2 fundamental deviations, compiled from saucecode/ISO286 (LGPL-2.1) and parkergreene/isofits (MIT), cross-checked cell-for-cell

Verified against parkergreene/isofits ISO 286-2 limit tables (MIT); ISO 286-1 formula harness — 2067 checks passed

Computed from the standard's formulas, then checked against published tables.

IT6 tolerance gradecompiled

ISO 286-1 IT grades and ISO 286-2 fundamental deviations, compiled from saucecode/ISO286 (LGPL-2.1) and parkergreene/isofits (MIT), cross-checked cell-for-cell

Verified against parkergreene/isofits ISO 286-2 limit tables (MIT); ISO 286-1 formula harness — 2067 checks passed. Formula per ISO 286-1 standard tolerance factor and fundamental deviation formulas, used as a validation harness only per docs/research/data-sourcing.md §3.6

Compiled from independent public sources that agree cell-for-cell.

H fundamental deviationcompiled

ISO 286-1 IT grades and ISO 286-2 fundamental deviations, compiled from saucecode/ISO286 (LGPL-2.1) and parkergreene/isofits (MIT), cross-checked cell-for-cell

Verified against parkergreene/isofits ISO 286-2 limit tables (MIT); ISO 286-1 formula harness — 2067 checks passed

Compiled from independent public sources that agree cell-for-cell.

Formula

Limits from the deviations, hole tolerance

max Ø  =  nominal + ES
min Ø  =  nominal + EI

  ES = upper deviation (µm)
  EI = lower deviation (µm)

The deviations are tabulated in ISO 286-2 and compiled here; the limits are those deviations added to the nominal size, which is why both columns are shown.

Assumptions

Values apply at the ISO 286 reference temperature of 20 °C.
Limits are for a plain cylindrical feature. A tolerance letter says nothing about surface finish, form or roundness — those need their own callouts.
Dataset scope: COMPILED not computed: the ISO 286-1 formula deviates up to 13.26% from the table and is used only as a harness (warn >5%, fail >15%). EXCLUDED: shaft/hole letters s, t, u and the fits H7/s6, H7/t6, H7/u6 — no free source and an undetermined step constant in the formula.

Data last verified

August 1, 2026

How this data is built and checked →

How to Cite This H6 Tolerance Reference

Citation

ShopMath. "H6 Tolerance — Hole Limits by Nominal Size." ShopMath, verified August 1, 2026, https://shopmath.org/fits/h6-hole

BibTeX

@misc{shopmath-fits-h6-hole,
  title        = {H6 Tolerance — Hole Limits by Nominal Size},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/fits/h6-hole}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/fits/h6-hole

Common Questions About the H6 Tolerance

What is the tolerance of a 25 mm H6 hole?: A 25 mm H6 hole runs 25.000 to 25.013 mm — deviations of 0 to +13 µm, a tolerance band 13 µm wide.
What does H6 mean?: H6 is an ISO 286 hole tolerance. The H sets the fundamental deviation — zero deviation — the basic hole — and the 6 is the IT6 tolerance grade, which sets how wide the band is. Precision basic hole for close-running and transition fits.
How wide is the IT6 tolerance band?: IT6 is 13 µm wide for nominal sizes over 18 up to 30 mm, and widens with size — the full band table is on this page.

Every ISO 286 designation and fit · ISO 286 tolerance chart