ISO 2768 Tolerance Class Finder

Enter a nominal size and the ± tolerance the feature really needs, and the finder lists the ISO 2768-1 general tolerance classes that hold it. It names the coarsest class that still works, which is the one to write in the title block. When no class is tight enough, the dimension needs its own tolerance on the drawing.

Units

Nominal size (mm)

Required Tolerance ± (mm)

Enter a nominal size and the ± tolerance the function needs.

Parts machined to your drawing

Zhenling quotes metal parts machined to your drawing. Send the drawing with the general tolerance note you settled on, plus any dimension that needs its own tolerance.

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How to read the result

Note to write names the coarsest class whose deviation at your size is no larger than the ± value you entered.
Covers your need compares the class deviation for your size range with your ± value, and an equal value counts as covered.
Your need ÷ class divides your ± value by the class deviation: 1 means the class uses your whole band, 2 means it uses half of it, and anything below 1 means the class is too loose.
No value in the table means ISO 2768-1 gives no deviation for that class at that size: class v has none up to 3 mm and class f has none above 2000 mm.
A general note governs every dimension on the drawing that carries no tolerance of its own, so run the finder on the untoleranced dimension with the tightest need.
Inch entries are converted at 1 in = 25.4 mm and compared in millimetres, the unit of the ISO 2768-1 table.

Why the coarsest class that works is the sensible choice

Every untoleranced dimension on the drawing inherits the class you write, not only the one you checked here.
A tighter class can add finishing passes on features whose function never asked for them.
Inspection has to prove the tighter band on each of those features, which adds measurement time per part.
The coarsest class that covers the need keeps close work where the function asks for it and lets the rest of the part run at the wider band.

Where the values come from

The deviations are the linear dimension values of ISO 2768-1:1989 for classes f (fine), m (medium), c (coarse) and v (very coarse). ISO last reviewed and confirmed this edition in 2022, and it lists a revised ISO 2768 as under development.

Size ranges run 0.5 up to 3 mm, then over 3 up to 6, over 6 up to 30, over 30 up to 120, over 120 up to 400, over 400 up to 1000, over 1000 up to 2000 and over 2000 up to 4000 mm. Each range includes its upper limit, so 30 mm sits in the over 6 up to 30 range.
For nominal sizes below 0.5 mm, Note 1 of ISO 2768-1 says the deviations shall be indicated adjacent to the relevant nominal size, so the finder returns no class.
Sizes above 4000 mm are outside the table.
External radii and chamfer heights use a separate table in ISO 2768-1 and are not part of this finder.
The second letter in notes such as ISO 2768-mK comes from ISO 2768-2:1989, which ISO withdrew on 4 February 2021 and revised as ISO 22081:2021. This finder covers only the linear classes of Part 1.

For design release, check the values against the edition of ISO 2768-1 named on your drawing.