ISO 2768-2 Straightness & Flatness Tolerances Table

This page shows the general tolerances for straightness and flatness according to ISO 2768-2, for features without individual geometrical tolerance indications. These values are typically applied to parts produced by material removal processes.

When general tolerances in accordance with ISO 2768 are used on a drawing, the indication should be written in or near the title block, e.g.: ISO 2768-mK or ISO 2768-fH, combining:

the linear dimensions tolerance class (f, m, c, v) from ISO 2768-1, and
the geometrical tolerance class (H, K, L) for straightness, flatness, perpendicularity, etc. from ISO 2768-2.

General tolerances on straightness and flatness (ISO 2768-2)

The following table gives the permissible deviations for straightness and flatness in millimetres, depending on the tolerance class (H, K, L) and the relevant length.

General Tolerances on Straightness and Flatness
Tolerance class	up to 10	over 10 up to 30	over 30 up to 100	over 100 up to 300	over 300 up to 1000	over 1000 up to 3000
H	0.02	0.05	0.1	0.2	0.3	0.4
K	0.05	0.1	0.2	0.4	0.6	0.8
L	0.1	0.2	0.4	0.8	1.2	1.6

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Note: values are in millimetres.

When a tolerance is selected, it shall be based on:

the length of the corresponding line for straightness, and
the longer lateral length of the surface or the diameter of the circular surface for flatness.

FAQ: general tolerances according to ISO 2768

What does “ISO 2768-mK” mean on a drawing?

The notation ISO 2768-mK combines: m = medium class for linear dimensions (ISO 2768-1) and K = general geometrical tolerance class (here including straightness and flatness) from ISO 2768-2.

When should I use general tolerances?

General tolerances are used for features where no individual tolerance is specified, but where a default level of accuracy must still be guaranteed. They simplify drawings and are suitable for typical machined parts where standard workshop practice is used.

Do ISO 2768-2 tolerances apply to all features?

ISO 2768-2 applies only to features without individual geometrical tolerance indications. If a specific straightness or flatness tolerance is specified on the drawing for a feature, that value takes precedence over the general tolerance.

For a complete list of ISO and ANSI standards, charts and calculators for limits, fits, allowances and tolerances, see the limits, fits and tolerances (ISO and ANSI systems) overview .

Reference

ISO 2768-2:1989 – General tolerances – Part 2: Geometrical tolerances for features without individual tolerance indications.