Drawings & TolerancesDimensional tolerances

ISO 2768 general tolerances

The tolerances that apply to every dimension on a drawing without its own tolerance. The f, m, c and v tables of ISO 2768-1 for lengths, radii, chamfers and angles, the H, K and L classes of the withdrawn ISO 2768-2, and the new edition about to replace Part 1.

LiveUpdated 11 October 20265 min read

Untoleranced dimensions under ISO 2768-mK

Tolerance classes in ISO 2768-1: f, m, c, v: 4
A 25 mm length under class m: ±0.2mm
A 45° chamfer with a 40 mm shorter leg, class m: ±0°30′
ISO 2768-2 withdrawn, replaced by ISO 22081: 2021

Most dimensions on a drawing carry no tolerance of their own. They are still toleranced: a note in or near the title block, such as ISO 2768-m, applies one table of general tolerances to all of them at once. The drawing stays readable, and the tight tolerances that are written out stand out as the ones that matter.

Status: an edition about to change

Look up a general tolerance

ISO 2768-1:1989 lookup. Choose the type of dimension and the class written on the drawing.

Linear dimensions

Permissible deviations in mm, for the four tolerance classes f (fine), m (medium), c (coarse) and v (very coarse):

Nominal size (mm)	f	m	c	v
0.5 to 3	±0.05	±0.1	±0.2	—
over 3 to 6	±0.05	±0.1	±0.3	±0.5
over 6 to 30	±0.1	±0.2	±0.5	±1
over 30 to 120	±0.15	±0.3	±0.8	±1.5
over 120 to 400	±0.2	±0.5	±1.2	±2.5
over 400 to 1000	±0.3	±0.8	±2	±4
over 1000 to 2000	±0.5	±1.2	±3	±6
over 2000 to 4000	—	±2	±4	±8

For sizes below 0.5 mm, the deviation is written next to the nominal size. A dash means no general tolerance is specified for that class and range.

Example. A 25 mm length on a drawing marked ISO 2768-m may lie between 24.8 and 25.2 mm. The same length under class f may lie between 24.9 and 25.1 mm.

The table as step lines on logarithmic axes. In every size range the deviation grows by a factor of 2 to 3 from f to m and from m to c, and by 1.7 to 2.1 from c to v. The points mark the example; hover to read the deviations at any size.

External radii and chamfer heights

Nominal size (mm)	f and m	c and v
0.5 to 3	±0.2	±0.4
over 3 to 6	±0.5	±1
over 6	±1	±2

Angles

Angular deviations depend on the length of the shorter side of the angle, in mm:

Shorter side (mm)	f and m	c	v
up to 10	±1°	±1°30′	±3°
over 10 to 50	±0°30′	±1°	±2°
over 50 to 120	±0°20′	±0°30′	±1°
over 120 to 400	±0°10′	±0°15′	±0°30′
over 400	±0°5′	±0°10′	±0°20′

Example. A 45° chamfer angle whose shorter leg is 40 mm, under class m, may lie between 44°30′ and 45°30′.

Angular deviations against the length of the shorter side; the longer the side, the smaller the permitted angle error. Over 400 mm the line is drawn to 1000 mm. The point marks the example.

Straightness and flatness (withdrawn ISO 2768-2)

ISO 2768-2 added general geometrical tolerances in three classes, H, K and L. A drawing note such as ISO 2768-mK combines class m from Part 1 with class K from Part 2. For straightness and flatness, by nominal length in mm:

Nominal length (mm)	H	K	L
up to 10	0.02	0.05	0.1
over 10 to 30	0.05	0.1	0.2
over 30 to 100	0.1	0.2	0.4
over 100 to 300	0.2	0.4	0.8
over 300 to 1000	0.3	0.6	1.2
over 1000 to 3000	0.4	0.8	1.6

Part 2 also gave classes for perpendicularity, symmetry and circular run-out. Because the part is withdrawn, new drawings should refer to ISO 22081 instead.

Using general tolerances well

Choose the class the shop can hold without effort. General tolerances are meant to be met by normal workshop accuracy; anything tighter belongs on the dimension itself.
Write out every tolerance that matters for function. Fits, bearing seats and sealing faces need their own tolerances; see ISO 286 fits.
State the standard and the class explicitly. “General tolerances ±0.1” without a standard leaves angles, radii and form undefined.

Sources (9)

Every value and quotation on this page comes from the documents below.