ISO 2768 Tolerance Chart (mK, fH, cL) + Free PDF

Quick Answer: What Is ISO 2768?

ISO 2768 is the international standard for general tolerances. It applies to linear sizes, angles and geometric features that have no individual tolerance called out on the drawing. ISO 2768-1 covers linear and angular dimensions in four classes (f fine, m medium, c coarse and v very coarse), and ISO 2768-2 covers geometric tolerances in three classes (H, K and L).

A callout like ISO 2768-mK means medium linear plus K-class geometric.

This chart lists ISO 2768 tolerance values in millimeters for: linear dimensions by nominal size range, angular dimensions by shorter-side length and geometric tolerances for straightness, flatness, perpendicularity and symmetry. Inputs are the nominal dimension and the tolerance class. The lookup tool returns the exact ± value from ISO 2768-1.

ISO 2768-mK at a Glance

A two-letter callout such as ISO 2768-mK combines one class from each part of the standard. The first letter is the ISO 2768-1 class for linear and angular dimensions (f fine, m medium, c coarse, v very coarse). The second letter is the ISO 2768-2 class for form and position (H, K or L, from tight to loose). mK is by far the most common callout on CNC drawings: medium linear tolerances with the middle geometric class. A one-letter callout such as ISO 2768-m sets only the linear and angular tolerances and gives form and position no general tolerance at all.

Everything below is read straight from the full tables further down the page. Values in millimetres.

Linear and angular, class m (the "m" in mK)

Nominal length (mm)	Linear tolerance	Angular tolerance for that length
0.5 to 3	±0.1	±1° (up to 10 mm)
3 to 6	±0.1	±1° (up to 10 mm)
6 to 30	±0.2	±1° to 10 mm, ±0°30′ for 10 to 50 mm
30 to 120	±0.3	±0°30′ to 50 mm, ±0°20′ for 50 to 120 mm
120 to 400	±0.5	±0°10′
400 to 1000	±0.8	±0°5′
1000 to 2000	±1.2	±0°5′
2000 to 4000	±2.0	±0°5′

Form and position, class K (the "K" in mK)

Feature length (mm)	Straightness and flatness	Perpendicularity	Symmetry	Circular run-out
Up to 10	0.05	0.4	0.6	0.2
10 to 30	0.1	0.4	0.6	0.2
30 to 100	0.2	0.4	0.6	0.2
100 to 300	0.4	0.6	0.6	0.2
300 to 1000	0.6	0.8	0.8	0.2
1000 to 3000	1.0	1.0	1.0	0.2

Example: a 50 mm wide machined block on an ISO 2768-mK drawing may measure 49.7 to 50.3 mm, its faces must be flat within 0.2 mm and a face perpendicular to the base must be within 0.4 mm. Other common pairings are fH for precision instrument parts, mH for tighter form on general parts and cL for welded or cast structures. Circular run-out is 0.1 for H, 0.2 for K and 0.5 for L at every size. Use the lookup tool for an exact value, or read the tolerance fit chart when a mating hole and shaft need a specified fit instead of a general tolerance.

ISO 2768-1 Linear Tolerances

These are the allowed deviations for linear dimensions like length, width, height, and diameter. All values are in millimeters. A dash means that class does not apply for that range.

Nominal Range (mm) ▲	f — Fine ▲	m — Medium ▲	c — Coarse ▲	v — Very Coarse ▲
0.5 – 3	±0.05	±0.1	±0.2	—
3 – 6	±0.05	±0.1	±0.3	±0.5
6 – 30	±0.1	±0.2	±0.5	±1.0
30 – 120	±0.15	±0.3	±0.8	±1.5
120 – 400	±0.2	±0.5	±1.2	±2.5
400 – 1000	±0.3	±0.8	±2.0	±4.0
1000 – 2000	±0.5	±1.2	±3.0	±6.0
2000 – 4000	—	±2.0	±4.0	±8.0

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ISO 2768-1 Angular Tolerances

These are the allowed deviations for angular dimensions. The shorter side of the angle sets which range to use. Values are shown in degrees and minutes of arc.

Nominal Length (mm) ▲	f — Fine ▲	m — Medium ▲	c — Coarse ▲	v — Very Coarse ▲
Up to 10	±1°	±1°	±1°30'	±3°
10 – 50	±0°30'	±0°30'	±1°	±2°
50 – 120	±0°20'	±0°20'	±0°30'	±1°
120 – 400	±0°10'	±0°10'	±0°15'	±0°30'
Over 400	±0°5'	±0°5'	±0°10'	±0°20'

ISO 2768-2 Geometric Tolerances

These tolerances control the shape and position of features. They apply when a drawing calls out ISO 2768-2. The uppercase letter (H, K, or L) sets the class. All values are in millimeters.

Straightness & Flatness

Nominal Range (mm)	H	K	L
Up to 10	0.02	0.05	0.1
10 – 30	0.05	0.1	0.2
30 – 100	0.1	0.2	0.4
100 – 300	0.2	0.4	0.8
300 – 1000	0.3	0.6	1.2
1000 – 3000	0.5	1.0	2.0

Perpendicularity

Nominal Range (mm)	H	K	L
Up to 100	0.2	0.4	0.6
100 – 300	0.3	0.6	1.0
300 – 1000	0.4	0.8	1.5
1000 – 3000	0.5	1.0	2.0

Symmetry

Nominal Range (mm)	H	K	L
Up to 100	0.5	0.6	0.6
100 – 300	0.5	0.6	1.0
300 – 1000	0.5	0.8	1.5
1000 – 3000	0.5	1.0	2.0

When to Use Each Tolerance Class

Class f (Fine) — Use for tight fits and precision parts. Good for bearing bores, mating surfaces, and high-accuracy assemblies. Needs careful CNC work.
Class m (Medium) — The most common class. Works well for general CNC machined parts. Most shops can hold these tolerances without extra effort.
Class c (Coarse) — Use for parts where fit is not critical. Good for covers, brackets, and non-mating features. Keeps cost low.
Class v (Very Coarse) — Use for rough parts, castings, or flame-cut pieces. Not common for CNC work. Only applies to larger sizes.
A drawing note like "ISO 2768-mK" means linear class m and geometric class K. This is the most common callout for machined parts.
A dash (—) in the table means that class does not apply for that size range.
These are general tolerances. They only apply to features that do not have a specific tolerance called out on the drawing.

Frequently Asked Questions

What is the difference between ISO 2768-m and ISO 2768-mK?

ISO 2768-m sets only the linear and angular general tolerances, class medium. ISO 2768-mK adds the K class from ISO 2768-2, so flatness, straightness, perpendicularity, symmetry and run-out are also controlled without individual callouts. Most CNC drawings use mK; m alone leaves part form uncontrolled.

What is the ISO 2768-mK tolerance for a 50 mm dimension?

±0.3 mm for the length (the 30 to 120 mm band of class m), with straightness and flatness held to 0.2 mm over that length (the 30 to 100 mm band of class K) and perpendicularity to 0.4 mm. The angular tolerance for a 50 mm feature is ±0°20′.

Does ISO 2768 apply to inch drawings?

No. ISO 2768 is defined in millimetres and assumes a metric drawing. Inch drawings in the United States normally state default tolerances in the title block under ASME Y14.5, for example ±0.005 in for two-place decimals and ±0.010 in for one-place. If you receive an inch drawing marked ISO 2768, convert the band limits: ISO 2768-m at 30 to 120 mm (±0.3 mm) is about ±0.012 in.

What is ISO 2768 and when should I use it?

ISO 2768 is a standard for general tolerances. It applies to linear and angular dimensions on machined parts. Use it when a drawing does not show a specific tolerance for a feature. It saves time by removing the need to add tolerances to every single dimension.

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

ISO 2768-1 covers linear and angular dimensions. It sets the allowed variation for lengths, widths, heights, and angles. ISO 2768-2 covers geometric tolerances like straightness, flatness, perpendicularity, and symmetry. A drawing often calls out both, such as ISO 2768-mK.

What does ISO 2768-mK mean on a drawing?

The lowercase letter is the linear tolerance class from ISO 2768-1. The uppercase letter is the geometric tolerance class from ISO 2768-2. So ISO 2768-mK means medium linear tolerances and K-class geometric tolerances. This is the most common callout for general machined parts.

Which ISO 2768 tolerance class should I pick for CNC machined parts?

For most CNC machined parts, class m (medium) works well. It matches what a good CNC machine can hold without extra effort. Use class f (fine) for tighter features. Use class c (coarse) for parts where fit is not critical, like covers or brackets.