What is the tolerance for a 25 mm H7 hole?

A Ø25 mm H7 hole is made between 25.0000 mm and 25.0210 mm — a deviation of 0 to +21 µm, which is the IT7 tolerance of 21 µm for the 18–30 mm size band. H is the hole-basis letter, so its lower deviation is zero at every size.

What clearance does H7/g6 give?

At a 25 mm nominal size, H7/g6 gives between 7 µm and 41 µm of clearance. Both figures are positive, so it is a clearance fit: the parts always assemble with a gap, and the shaft can turn and slide. The clearance changes with the size band, so use the calculator for the size you are working at.

How do you calculate an ISO 286 fit?

Look up the standard tolerance IT for the grade in the size band containing your nominal size, and the fundamental deviation for the letter in the same band. The tabulated deviation is the one nearer the zero line; the other end of the zone is that value plus or minus IT. Then max clearance = hole upper deviation − shaft lower deviation, and min clearance = hole lower deviation − shaft upper deviation. If both are positive it is a clearance fit, if both are negative an interference fit, and if the range straddles zero a transition fit.

What is the difference between a hole-basis and a shaft-basis fit?

In a hole-basis fit the hole is H — its lower deviation is zero — and the shaft letter provides the clearance or interference. In a shaft-basis fit the shaft is h and the hole letter does the work. Hole basis is the usual choice because a hole is produced by a fixed-size tool such as a reamer, so it is cheaper to vary the shaft. Shaft basis suits drawn stock, or a single shaft that carries several parts needing different fits along its length.

Why does this calculator sometimes disagree with an ISO 286 formula calculator?

Because ISO 286-1 rounds its computed tolerances to preferred numbers before publishing them. Evaluating the standard tolerance factor directly reproduces the published table only approximately — up to 13.26% off in the 1–3 mm band and several percent off in others. This calculator reads the compiled table, so it matches a printed ISO 286-2 chart rather than the formula that approximately generates it.

What size range does this ISO 286 calculator cover?

Nominal sizes from 1 to 500 mm, in grades IT5 through IT12, across 17 hole letters and 17 shaft letters. Sizes above 500 mm use a different standard tolerance factor and are not in these tables — the calculator refuses them rather than extrapolating a number the standard does not publish.

Calculator · fits & tolerances

ISO 286 Limits & Fits Calculator — Hole and Shaft Tolerances

https://shopmath.org/calculators/iso-fit · data verified August 1, 2026

A Ø25 mm H7/g6 fit puts the hole between 25.0000 and 25.0210 mm and the shaft between 24.9800 and 24.9930 mm, leaving 7 to 41 µm of clearance — a clearance fit. Change the size or the designation below and the limits, the classification and the to-scale diagram all move with it.

Size range: 1–500 mm
Grades: IT5–IT12
Hole letters: 17
Shaft letters: 17
Named fits: 16
Verified: August 1, 2026

ISO 286 Limits and Fits Calculator — Any Size, Any Designation

Sixteen named fits, or build your own pair from 17 hole letters and 17 shaft letters across IT5 to IT12. Every value is read out of the compiled ISO 286-2 table — nothing is computed from the tolerance formula, which misses the published table by up to 13%.

ISO 286 limits and fits calculator

Fit

Nominal sizemm

Band 25.000 mm falls in — bands are “over X, up to and including Y”.

Named fit

Sliding. Locates accurately, still moves and turns freely.

H7/g6 at Ø25.000 mm · ISO 286

clearance

H7/g6

hole-basis fit — the hole is the reference

Max clearance: 41µm
Min clearance: 7µm
Hole IT: 21µm
Shaft IT: 13µm

The hole is always larger than the shaft. The parts always assemble. Sliding. Locates accurately, still moves and turns freely.

Tolerance zones for H7/g6 at 25.000 mm, drawn to scale in micrometres against the zero line. The hatched zone is the hole, the solid one the shaft. Where they overlap vertically, the shaft can come out larger than the hole — that overlap is what makes a fit a transition or an interference fit.

Hole and shaft limits for H7/g6 at Ø25.000 mm
Property	Limits of size		Deviations		Property
Feature	Max Ø mm	Min Ø mm	Upper µm	Lower µm	IT µm
Hole H7	25.0210	25.0000	+21	0	21
Shaft g6	24.9930	24.9800	-7	-20	13

Deviations are in micrometres from the nominal size; limits of size are the finished diameters in millimetres. The IT column is the standard tolerance — the height of each zone — for that grade in the size band containing 25.000 mm. Values come from the compiled ISO 286-2 table, not from the ISO 286-1 formula.

Reading it out loud

A Ø25.000 H7 hole is made between 25.0000 and 25.0210 mm. A Ø25.000 g6 shaft is made between 24.9800 and 24.9930 mm. Put the largest hole on the smallest shaft and you get 41 µm of clearance; put the smallest hole on the largest shaft and you get 7 µm of clearance. That is a clearance fit.

The formula, with your numbers in it

ISO 286-1, ISO 286-2

hole max = D + ES ÷ 1000        hole min = D + EI ÷ 1000
shaft max = D + es ÷ 1000       shaft min = D + ei ÷ 1000

hole max = 25 + +21 ÷ 1000 = 25.0210 mm
hole min = 25 + 0 ÷ 1000 = 25.0000 mm
shaft max = 25 + -7 ÷ 1000 = 24.9930 mm
shaft min = 25 + -20 ÷ 1000 = 24.9800 mm

The deviations are read out of the ISO 286-2 table for the H7 hole and the g6 shaft in the size band containing 25.000 mm. The tables carry EI for the hole and es for the shaft; the other end of each zone is that value plus or minus the IT tolerance.

```
max clearance = hole max − shaft min = ES − ei
min clearance = hole min − shaft max = EI − es
```
```
max clearance = +21 − (-20) = 41 µm
min clearance = 0 − (-7) = 7 µm
```
= clearance fit
A negative clearance is interference. Both positive is a clearance fit, both negative an interference fit, and a range that straddles zero is a transition fit — which is the entire classification rule.

A Worked ISO 286 Example — H7/g6 at Ø25 mm

The default state of the calculator above, written out — so the page carries a complete answer with or without JavaScript.

At a 25 mm nominal size, IT7 is 21 µm wide and IT6 is 13 µm wide. Both come from the 18–30 mm band — ISO 286 bands are stated as “over 18, up to and including 30”, so a 25 mm feature and a 30 mm feature share a tolerance while a 30.01 mm feature does not.

The H hole has a fundamental deviation of zero, so the H7 hole runs from 25.0000 mm to 25.0210 mm — the zero line is its lower limit, which is what “hole basis” means. The g shaft has a fundamental deviation of -7 µm, so the g6 shaft runs from 24.9800 mm to 24.9930 mm, entirely below the zero line.

Largest hole on smallest shaft gives 41 µm of clearance; smallest hole on largest shaft gives 7 µm. Both are positive, so the parts always assemble with a gap: a clearance fit. The shaft can still turn and slide, which is what H7/g6 is chosen for.

What an Interference Fit Looks Like — H7/p6 at Ø25 mm

Same hole, a different shaft letter, and the zones now overlap.

The H7 hole has not moved. The p shaft sits entirely above the zero line, from 25.0220 mm to 25.0350 mm, so even the smallest shaft is larger than the smallest hole. Clearance runs from -1 µm to -35 µm — both negative, which is interference by another name, and the reason assembly needs a press or a temperature difference.

Tolerance zones for H7/p6 at 25.000 mm, drawn to scale in micrometres against the zero line. The hatched zone is the hole, the solid one the shaft. Where they overlap vertically, the shaft can come out larger than the hole — that overlap is what makes a fit a transition or an interference fit.

The Sixteen Named ISO 286 Fits, Compared at Ø25 mm

Every preset in the calculator, ordered from the loosest running fit to the heaviest drive fit, so the whole ladder is visible at one size.

Named ISO 286 fits and their clearance range at a 25 mm nominal size
Property	Property	Clearance at Ø25 mm, µm		Property
Fit	Type	Min	Max	What it is for
H11/c11	clearance	110	370	Loose running. Wide commercial tolerances, large clearance for dirt, paint and thermal growth.
H9/d9	clearance	65	169	Free running. Good where accuracy is not essential and clearance can be generous.
H8/e8	clearance	40	106	Running fit with room for a lubricant film at speed.
H8/f7	clearance	20	74	Close running. The general-purpose lubricated journal fit.
F8/h7	clearance	20	74	Close running, shaft basis.
H7/g6	clearance	7	41	Sliding. Locates accurately, still moves and turns freely.
G7/h6	clearance	7	41	Sliding, shaft basis. The h6 shaft is the reference and the hole carries the clearance.
H7/h6	clearance	0	34	Locational clearance. Assembles by hand, no free movement intended.
H7/k6	transition	-15	19	Locational transition. Accurate location, assembles with light force.
K7/h6	transition	-15	19	Locational transition, shaft basis.
H7/m6	transition	-21	13	Locational transition, tighter than k6.
H7/n6	transition	-28	6	Tight transition. Usually a press job.
N7/h6	transition	-28	6	Tight transition, shaft basis.
H7/p6	interference	-35	-1	Locational interference. Rigid location in steel without the load capacity of a drive fit.
P7/h6	interference	-35	-1	Locational interference, shaft basis.
H7/r6	interference	-41	-7	Medium drive. The joint itself carries load.

Clearance figures are for a 25 mm nominal size; they scale with the size band, so use the calculator for the size in front of you. Negative clearance is interference. Hole-basis fits keep the hole at H and move the shaft, which is the usual choice because a hole is made by a fixed-size tool; shaft-basis fits do the reverse and are for drawn stock or a shaft that carries several different parts.

Sources and Method for the ISO 286 Fit Calculator

ISO 286 tablescompiled

saucecode/ISO286 (LGPL-2.1) + parkergreene/isofits (MIT), cross-checked cell-for-cell

Verified against fits-iso286: 2067 checks passed across 3 harness(es)

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

Formula

Limits of size from the tabulated deviations

hole max  =  D + ES ÷ 1000        hole min  =  D + EI ÷ 1000
shaft max =  D + es ÷ 1000        shaft min =  D + ei ÷ 1000

  D = nominal size (mm)
  ES, EI = upper and lower deviation of the hole (µm)
  es, ei = upper and lower deviation of the shaft (µm)

The deviation the table does not print

holes A–H:  ES = EI + IT        holes J–R:  EI = ES − IT
shafts a–h: ei = es − IT        shafts j–r: es = ei + IT

ISO 286-2 tabulates only the deviation nearer the zero line; the other end of the zone is that value plus or minus the standard tolerance for the grade.

Clearance and the classification

max clearance  =  hole max − shaft min  =  ES − ei
min clearance  =  hole min − shaft max  =  EI − es

  min ≥ 0            -> clearance fit
  max ≤ 0            -> interference fit
  otherwise          -> transition fit

A negative clearance is interference. This is why the calculator can classify a pair that appears in no published fit table.

Assumptions

Values are COMPILED from two independent open datasets that agree cell-for-cell, not computed. The ISO 286-1 formula deviates from the published table by up to 13.26% and is retained as a validation harness only.
Size bands are ranges, stated as 'over X, up to and including Y'. A 30 mm feature uses the 18–30 band and a 30.01 mm feature uses 30–50. Nothing is interpolated between bands, because the standard does not interpolate.
Coverage is 1–500 mm and grades IT5–IT12. Sizes above 500 mm use a different tolerance factor entirely and are not in these tables; the calculator refuses rather than extrapolating.
Shaft and hole letters s, t and u — and the fits H7/s6, H7/t6, H7/u6 — are excluded. No free source was available and the formula has an undetermined step constant, so shipping them would mean shipping a guess.
Deviations for the letters j to r and J to R depend on the tolerance grade, and only the grades that are tabulated are offered. The composite letters CD, EF and FG exist only at the small end and disappear above 10 mm.
These are dimensional limits only. Surface finish, form error, temperature and the assembly method all affect a real fit and none of them are in this calculation.
ISO 286 tables 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 ISO 286 Fit Calculator

Citation

ShopMath. "ISO 286 Limits & Fits Calculator — Hole and Shaft Tolerances." ShopMath, verified August 1, 2026, https://shopmath.org/calculators/iso-fit

BibTeX

@misc{shopmath-calculators-iso-fit,
  title        = {ISO 286 Limits & Fits Calculator — Hole and Shaft Tolerances},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/calculators/iso-fit}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/calculators/iso-fit

Common Questions About ISO 286 Limits and Fits

What is the tolerance for a 25 mm H7 hole?: A Ø25 mm H7 hole is made between 25.0000 mm and 25.0210 mm — a deviation of 0 to +21 µm, which is the IT7 tolerance of 21 µm for the 18–30 mm size band. H is the hole-basis letter, so its lower deviation is zero at every size.
What clearance does H7/g6 give?: At a 25 mm nominal size, H7/g6 gives between 7 µm and 41 µm of clearance. Both figures are positive, so it is a clearance fit: the parts always assemble with a gap, and the shaft can turn and slide. The clearance changes with the size band, so use the calculator for the size you are working at.
How do you calculate an ISO 286 fit?: Look up the standard tolerance IT for the grade in the size band containing your nominal size, and the fundamental deviation for the letter in the same band. The tabulated deviation is the one nearer the zero line; the other end of the zone is that value plus or minus IT. Then max clearance = hole upper deviation − shaft lower deviation, and min clearance = hole lower deviation − shaft upper deviation. If both are positive it is a clearance fit, if both are negative an interference fit, and if the range straddles zero a transition fit.
What is the difference between a hole-basis and a shaft-basis fit?: In a hole-basis fit the hole is H — its lower deviation is zero — and the shaft letter provides the clearance or interference. In a shaft-basis fit the shaft is h and the hole letter does the work. Hole basis is the usual choice because a hole is produced by a fixed-size tool such as a reamer, so it is cheaper to vary the shaft. Shaft basis suits drawn stock, or a single shaft that carries several parts needing different fits along its length.
Why does this calculator sometimes disagree with an ISO 286 formula calculator?: Because ISO 286-1 rounds its computed tolerances to preferred numbers before publishing them. Evaluating the standard tolerance factor directly reproduces the published table only approximately — up to 13.26% off in the 1–3 mm band and several percent off in others. This calculator reads the compiled table, so it matches a printed ISO 286-2 chart rather than the formula that approximately generates it.
What size range does this ISO 286 calculator cover?: Nominal sizes from 1 to 500 mm, in grades IT5 through IT12, across 17 hole letters and 17 shaft letters. Sizes above 500 mm use a different standard tolerance factor and are not in these tables — the calculator refuses them rather than extrapolating a number the standard does not publish.