ISO 2768 General Tolerance Calculator.
Look up the general tolerance that applies to every unspecified dimension on your drawing. Covers ISO 2768-1 linear, angular and chamfer tolerances (classes f, m, c, v) and ISO 2768-2 geometric tolerances (classes H, K, L).
Drawing Note
Feature Being Checked
A dimension with its own tolerance overrides the general note entirely.
Part 1 class letter is lower case (f/m/c/v); Part 2 is upper case (H/K/L).
What ISO 2768 Actually Controls
ISO 2768 is the general-tolerance standard that silently governs most of a mechanical drawing. Any dimension left without its own tolerance inherits the class named in the title block. On a typical machined part that is 80–90% of all dimensions, which is why a wrong class letter can quietly change scrap rate across an entire production run.
The standard has two parts, and a complete callout names one class from each:
- ISO 2768-1 — linear and angular dimensions. Classes f (fine), m (medium), c (coarse), v (very coarse).
- ISO 2768-2 — geometric tolerances: straightness, flatness, perpendicularity, symmetry, run-out. Classes H, K, L.
So ISO 2768-mK means medium dimensional tolerances plus class K geometric tolerances. ISO 2768-m alone invokes Part 1 only, and leaves form and orientation uncontrolled — a common and expensive drawing omission.
ISO 2768-1 — Linear Dimensions (mm)
| Nominal size | f — fine | m — medium | c — coarse | v — very coarse |
|---|---|---|---|---|
| 0.5 – 3 | ±0.05 | ±0.1 | ±0.2 | — |
| over 3 – 6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 |
| over 6 – 30 | ±0.1 | ±0.2 | ±0.5 | ±1.0 |
| over 30 – 120 | ±0.15 | ±0.3 | ±0.8 | ±1.5 |
| over 120 – 400 | ±0.2 | ±0.5 | ±1.2 | ±2.5 |
| over 400 – 1000 | ±0.3 | ±0.8 | ±2.0 | ±4.0 |
| over 1000 – 2000 | ±0.5 | ±1.2 | ±3.0 | ±6.0 |
| over 2000 – 4000 | — | ±2.0 | ±4.0 | ±8.0 |
ISO 2768-1 — External Radii and Chamfer Heights (mm)
| Nominal size | f | m | c | v |
|---|---|---|---|---|
| 0.5 – 3 | ±0.2 | ±0.2 | ±0.4 | ±0.4 |
| over 3 – 6 | ±0.5 | ±0.5 | ±1.0 | ±1.0 |
| over 6 | ±1.0 | ±1.0 | ±2.0 | ±2.0 |
ISO 2768-1 — Angular Tolerances
Angular tolerance is set by the length of the shorter leg of the angle, not by the angle value.
| Shorter leg (mm) | f | m | c | v |
|---|---|---|---|---|
| up to 10 | ±1° | ±1° | ±1°30' | ±3° |
| over 10 – 50 | ±0°30' | ±0°30' | ±1° | ±2° |
| over 50 – 120 | ±0°20' | ±0°20' | ±0°30' | ±1° |
| over 120 – 400 | ±0°10' | ±0°10' | ±0°15' | ±0°30' |
| over 400 | ±0°5' | ±0°5' | ±0°10' | ±0°20' |
ISO 2768-2 — Straightness and Flatness (mm)
| Nominal length | H | K | L |
|---|---|---|---|
| up to 10 | 0.02 | 0.05 | 0.1 |
| over 10 – 30 | 0.05 | 0.1 | 0.2 |
| over 30 – 100 | 0.1 | 0.2 | 0.4 |
| over 100 – 300 | 0.2 | 0.4 | 0.8 |
| over 300 – 1000 | 0.3 | 0.6 | 1.2 |
| over 1000 – 3000 | 0.4 | 0.8 | 1.6 |
ISO 2768-2 — Perpendicularity, Symmetry and Run-out (mm)
| Characteristic / range | H | K | L |
|---|---|---|---|
| Perpendicularity — up to 100 | 0.2 | 0.4 | 0.6 |
| Perpendicularity — over 100 – 300 | 0.3 | 0.6 | 1.0 |
| Perpendicularity — over 300 – 1000 | 0.4 | 0.8 | 1.5 |
| Perpendicularity — over 1000 – 3000 | 0.5 | 1.0 | 2.0 |
| Symmetry — up to 100 | 0.5 | 0.6 | 0.6 |
| Symmetry — over 100 – 300 | 0.5 | 0.6 | 1.0 |
| Symmetry — over 300 – 1000 | 0.5 | 0.8 | 1.5 |
| Symmetry — over 1000 – 3000 | 0.5 | 1.0 | 2.0 |
| Circular run-out — all sizes | 0.1 | 0.2 | 0.5 |
Worked Example
A drawing carries the note ISO 2768-mK. A boss is dimensioned 120 mm with no tolerance shown, and its face has no flatness callout.
- 120 falls in the over 30 – 120 band → class m gives ±0.3 mm, so limits are 119.7 / 120.3.
- Flatness on a 120 mm face falls in over 100 – 300 → class K gives 0.4 mm.
- A 2 mm chamfer inherits ±0.2 mm from the radius table.
- A 45° angle whose shorter leg is 20 mm inherits ±0°30'.
Note the trap: 120 sits exactly on a band boundary. The bands read "over 30 up to and including 120", so 120 takes ±0.3, not the ±0.5 of the next band. Getting this backwards is one of the most common inspection disputes.
Choosing the Right Class
- f (fine) — precision machining, jig and fixture work, instrument parts. Expensive on large dimensions.
- m (medium) — the default for general machining and most fabricated assemblies. Use this unless you have a reason not to.
- c (coarse) — flame-cut, welded, and heavy fabricated structures.
- v (very coarse) — castings, forgings and rough structural work before machining.
Specifying f across a whole drawing to "be safe" is a classic cost error: it tightens hundreds of dimensions that never needed control, and every one becomes an inspection point. Tolerance the few features that matter individually and leave the rest at m.
ISO 2768 vs ISO 286
The two standards do different jobs. ISO 2768 is a blanket rule for unspecified dimensions. ISO 286 defines the IT grades and fit classes (H7, g6, and so on) that you apply deliberately to mating features. A shaft that must run in a bearing gets an ISO 286 fit; the chamfer at its end gets ISO 2768. On the equivalence: class m is broadly comparable to IT12–IT14 depending on size, and class f to roughly IT11–IT12 — close enough for planning, never close enough to substitute one callout for the other.
Related Tools
For deliberate fits on mating features, use the ISO 286 Fits Calculator. To confirm the general tolerances still close your assembly, run a Tolerance Stack-Up. For positional callouts see Position Tolerance, and for surface texture limits see Surface Finish.