ISO 2768 Tolerance Calculator & Tables

If a drawing states “General tolerances ISO 2768-mK”, the table values of the standard apply to all dimensions without an individual tolerance indication. The first letter designates the tolerance class for linear and angular dimensions per ISO 2768-1 (f, m, c or v), the second the class for form and location per ISO 2768-2 (H, K or L). In Switzerland the standard is adopted as SN EN ISO 2768.

ISO 2768-1: limit deviations for linear dimensions

The limit deviations apply per nominal size range, symmetrically as a ± value. For nominal sizes below 0.5 mm, the tolerance must be indicated directly at the dimension.

Broken edges (chamfers and edge radii) have their own, coarser table:

ISO 2768-1: limit deviations for angular dimensions

Decisive is the length of the shorter leg of the angle — not the nominal angle.

ISO 2768-2: form and location — classes H, K, L

Part 2 defines general tolerances for straightness, flatness, perpendicularity, symmetry and run-out. For straightness and flatness, the longer value of the considered line or surface applies:

Perpendicularity — the shorter leg is decisive:

Symmetry — the longer value is decisive:

Run-out (circular and axial run-out) is independent of the nominal size: 0.1 mm in class H, 0.2 mm in class K and 0.5 mm in class L.

What is ISO 2768?

ISO 2768 defines general tolerances: limit values that apply to every dimension on a drawing that carries no individual tolerance indication. Part 1 covers linear and angular dimensions, Part 2 covered form and location. The note sits in or near the title block, for example “General tolerances ISO 2768-mK”.

Its purpose is relief: uncritical dimensions need no individual tolerancing, the drawing stays readable, and the shop still has a binding limit for every dimension.

What do f, m, c and v mean — and H, K, L?

The lower-case letters are the tolerance classes for linear and angular dimensions per Part 1, the upper-case letters the classes for form and location per Part 2:

• f (fine) — precision parts with elevated requirements.
• m (medium) — normal workshop accuracy of machining; by far the most common class.
• c (coarse) — for example welded structures and formed parts.
• v (very coarse) — rough production processes; not defined below 3 mm nominal size.
• H, K, L — form and location tolerances from tight (H) to coarse (L); K is widespread.

What does ISO 2768-mK mean?

“ISO 2768-mK” combines two indications: m is the medium tolerance class for linear and angular dimensions per ISO 2768-1, K the class for form and location per ISO 2768-2. A 50 mm dimension without its own tolerance thus gets ±0.3 mm; the flatness of an 80 mm surface 0.2 mm.

On new drawings the geometry part belongs in ISO 22081 today. On countless existing drawings, however, “-mK” remains binding and must be read correctly.

Can ISO 2768 still be applied today?

Part 1 of 1989 remains decisive until the new edition appears. The revision narrows the scope considerably — and thereby changes what an undated reference to “ISO 2768” will mean in the future.

ISO 2768-2:1989 has been replaced by ISO 22081:2021. For new drawings, general geometrical specifications therefore belong in ISO 22081 — with an explicitly stated datum. On countless existing drawings, however, the indication per ISO 2768-2 remains a reality and must be interpreted correctly when inspecting.

Dated and undated references

A dated reference (“ISO 2768-1:1989”) freezes the edition: exactly this issue applies, even if the standard is later replaced. An undated reference (“ISO 2768-1” or just “ISO 2768-mK”) means the current edition applies — the drawing changes its meaning as soon as a new edition appears or a part is withdrawn.

Exactly that is happening to ISO 2768 right now. Why this is critical for existing drawings and how to protect legacy stock: ISO/FDIS 2768 — why the undated application is critical.

Worked examples

Example 1 — drawing note “50 ISO 2768-m”

Nominal size 50 mm falls in the range over 30 to 120 mm. Class m gives ±0.3 mm: lower limit of size 49.7 mm, upper limit of size 50.3 mm. Any measured value within these limits conforms.

Example 2 — title block “ISO 2768-mK”

Every dimension without its own tolerance gets the m value of its size range, and form and location are limited by the K tables — for example flatness 0.2 mm on an 80 mm surface, perpendicularity 0.4 mm on a 60 mm leg.

Example 3 — legacy drawing from 2012, only “ISO 2768-mK”

The reference is undated. As long as both parts were in force, it was unambiguous. Today Part 2 is withdrawn and Part 1 is about to be replaced — so the interpretation depends on the drawing date, the agreed edition and the GPS system in use. Agree in writing which edition applies before measuring or rejecting.

Common mistakes on technical drawings

• The general tolerance applies only without an individual indication. As soon as a dimension carries its own tolerance, the table no longer applies to that dimension.
• Clarify the class and the edition. “ISO 2768” without a class or without a date is not an unambiguous specification — and with disputed dimensions, exactly that becomes the problem.
• Angles looked up by nominal angle. Decisive is the length of the shorter leg, not the number of degrees.
• Dimensions below 0.5 mm left to the general tolerance. ISO 2768-1 does not apply there — the tolerance belongs directly at the dimension.
• A general tolerance does not replace function-oriented tolerancing. Function-critical characteristics belong toleranced individually — per ISO GPS with datums and a clear specification, if needed with support in the project.
• Rejection per ISO 2768-1 is not automatic. The standard notes that exceeding the general tolerance does not necessarily lead to rejection if the function is not impaired — this too belongs cleanly agreed rather than silently assumed.

Frequently asked questions about ISO 2768

What does ISO 2768 mean?

The standard for general tolerances: it provides limit values for all dimensions without an individual tolerance indication. Part 1 (linear and angular dimensions) is valid, Part 2 (form and location) is withdrawn.

What does ISO 2768-m mean?

Tolerance class medium per Part 1. The ± value depends on the nominal size range: 50 mm → ±0.3 mm, 200 mm → ±0.5 mm, 500 mm → ±0.8 mm.

What does ISO 2768-mK mean?

m is the class for linear and angular dimensions (Part 1), K the class for form and location (Part 2) — the most common combination. Details in the section What does ISO 2768-mK mean?

Which tolerance applies at 50 mm?

Depending on the class: f ±0.15 mm, m ±0.3 mm, c ±0.8 mm, v ±1.5 mm.

Is ISO 2768 still valid?

Part 1: yes — 1989 edition, confirmed 2022; the new edition is imminent. Part 2: withdrawn, replaced for new drawings by ISO 22081:2021.

May ISO 2768 be used on new drawings?

Part 1 yes — preferably with a dated reference “ISO 2768-1:1989”, so the new edition does not silently change the meaning. Geometry belongs specified via ISO 22081 on new drawings.

What happens with an undated reference?

The current edition applies. When a new edition appears or a part is withdrawn, the drawing changes its meaning — without a single line on it changing.

What is the difference between ISO 2768-1 and ISO 2768-2?

Part 1 tolerances linear and angular dimensions (classes f, m, c, v). Part 2 tolerated form and location — straightness, flatness, perpendicularity, symmetry, run-out (classes H, K, L).

Which standard replaces ISO 2768?

For form and location: ISO 22081:2021. For Part 1, ISO/TC 213 has a new edition of ISO 2768 in the final production steps (status August 2026).

Does ISO 2768 apply to all dimensions?

No. Only to dimensions without an individual tolerance, and only from 0.5 mm. Dimensions with their own tolerance, auxiliary dimensions in parentheses and theoretically exact dimensions are excluded.

How are angles handled?

Via the length of the shorter leg: up to 10 mm class m gives ±1°, over 400 mm only ±0° 5′.

Unclear what really applies on your drawing? CSL reviews drawings for unambiguity, conformity to the standards and verifiability — and measures your parts with a clear conformity decision per characteristic.