General tolerances (ISO 2768)
Under ISO 2768-m (medium), a 50 mm untoleranced linear dimension carries ±0.3 mm — that is 49.7 to 50.3 mm without a single tolerance drawn on the print. This page returns the general tolerance for any nominal dimension by class (f, m, c, v) and feature type, from ISO 2768-1 (linear and angular, current) and the withdrawn ISO 2768-2 (geometrical, shown as legacy).
A title-block note like “ISO 2768-mK” sets the class that applies to every dimension carrying no explicit tolerance. The band widens with the nominal size, so the same class gives ±0.1 mm at 3 mm and ±0.8 mm at 1000 mm.
The length itself
Title block · general tolerances
ISO 2768-mK
Looking it up…
How it’s calculated
A drawing's general-tolerance note gives two classes: the lower-case letter for sizes (linear sizes, external radii and chamfer heights, and angles: Part 1, Tables 1 to 3) and the capital for geometry (straightness and flatness, perpendicularity, symmetry, runout: Part 2, Tables 1 to 4, withdrawn in 2021 and shown as legacy). Each table steps by size: the row is the one the length is over the minimum of, up to and including its maximum. The length is not always the dimension: an angle is looked up by its shorter leg; straightness and flatness by the length of the line or the longer side of the surface; perpendicularity by the shorter of its two sides; symmetry by the longer of its two features; runout needs no length at all. A geometrical value is the full width of the zone, never ±. A tolerance drawn on a dimension always overrides the general one. DIN 7168 is the withdrawn German predecessor (size classes f, m, g, sg; geometry R, S, T, U, with no perpendicularity table), shown for old prints.
What does an ISO 2768 class mean?
ISO 2768-1 defines four tolerance classes for linear and angular dimensions — f (fine), m (medium), c (coarse), and v (very coarse) — each a table of ± values banded by nominal size. A drawing invokes one class in the title block so that dimensions without their own tolerance are still controlled, rather than left open.
ISO 2768-2 added general geometrical tolerances (straightness, flatness, perpendicularity, symmetry, runout) in three classes H, K, L. A callout such as ISO 2768-mK means class m for size and class K for form and geometry. Each geometrical value is the total width of the tolerance zone, not a ± limit.
ISO 2768-2 was withdrawn in February 2021 and superseded by ISO 22081:2021, which publishes no H/K/L value table. Drawings that cite it are still made and checked, so its values are shown here, labelled legacy; they are not current.
How does DIN 7168 relate to ISO 2768?
DIN 7168 is the withdrawn German predecessor that ISO 2768 superseded; its medium/coarse linear tables are close to ISO 2768-m/-c, but its radius and chamfer table is not (five bands to 400 mm against ISO’s three). This page shows it, labelled legacy, so an older print citing DIN 7168 can be checked; for new work ISO 2768-1 governs.