ISO 2768 calculator
Enter a nominal size and the class from your title block. You get the permitted deviation for linear sizes, radii and chamfers, angles and, with a form class, the geometric tolerances from ISO 2768-2.
ISO 2768 starts at 0.5 mm. Below that, the drawing has to state a tolerance itself.
- Linear size
- ± 0.3 mm (49.7 … 50.3 mm)
- Radius / chamfer height
- ± 1 mm
- Angle (size = shorter leg)
- ± 0°30′
- Straightness and flatness
- 0.2 mm
- Perpendicularity (size = shorter side)
- 0.4 mm
- Symmetry
- 0.6 mm
- Circular run-out
- 0.2 mm
For angles the standard uses the length of the shorter leg, for perpendicularity the shorter side. Here the entered size is used for both.
ISO 2768 tables
All values in mm unless stated otherwise. Range limits are inclusive: "over 3 to 6" includes 6.
| Nominal size (mm) | 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 |
| over 30 – 120 | ± 0.15 | ± 0.3 | ± 0.8 | ± 1.5 |
| over 120 – 400 | ± 0.2 | ± 0.5 | ± 1.2 | ± 2.5 |
| over 400 – 1,000 | ± 0.3 | ± 0.8 | ± 2 | ± 4 |
| over 1,000 – 2,000 | ± 0.5 | ± 1.2 | ± 3 | ± 6 |
| over 2,000 – 4,000 | – | ± 2 | ± 4 | ± 8 |
| Nominal size (mm) | f and m | c and v |
|---|---|---|
| 0.5 – 3 | ± 0.2 | ± 0.4 |
| over 3 – 6 | ± 0.5 | ± 1 |
| > 6 | ± 1 | ± 2 |
| Shorter leg (mm) | f and m | c (coarse) | v (very coarse) |
|---|---|---|---|
| ≤ 10 | ± 1° | ± 1°30′ | ± 3° |
| over 10 – 50 | ± 0°30′ | ± 1° | ± 2° |
| over 50 – 120 | ± 0°20′ | ± 0°30′ | ± 1° |
| over 120 – 400 | ± 0°10′ | ± 0°15′ | ± 0°30′ |
| > 400 | ± 0°5′ | ± 0°10′ | ± 0°20′ |
| Nominal size (mm) | H | K | L |
|---|---|---|---|
| ≤ 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 – 1,000 | 0.3 | 0.6 | 1.2 |
| over 1,000 – 3,000 | 0.4 | 0.8 | 1.6 |
| Shorter side (mm) | H | K | L |
|---|---|---|---|
| ≤ 100 | 0.2 | 0.4 | 0.6 |
| over 100 – 300 | 0.3 | 0.6 | 1 |
| over 300 – 1,000 | 0.4 | 0.8 | 1.5 |
| over 1,000 – 3,000 | 0.5 | 1 | 2 |
| Nominal size (mm) | H | K | L |
|---|---|---|---|
| ≤ 100 | 0.5 | 0.6 | 0.6 |
| over 100 – 300 | 0.5 | 0.6 | 1 |
| over 300 – 1,000 | 0.5 | 0.8 | 1.5 |
| over 1,000 – 3,000 | 0.5 | 1 | 2 |
| H | K | L |
|---|---|---|
| 0.1 | 0.2 | 0.5 |
Source: ISO 2768-1:1989 and ISO 2768-2:1989. Check the edition referenced on your drawing for critical parts.
Why general tolerances exist
Without a general tolerance you'd have to tolerance every dimension separately — unworkable. ISO 2768 fixes one class that sets the allowed deviation for all free dimensions, depending on size. Only functionally critical dimensions then get their own tighter tolerance.
ISO 2768-1 vs -2
Part 1 (f/m/c/v) covers linear and angular dimensions. Part 2 (H/K/L) covers form and position tolerances like flatness and squareness. ISO 2768-mK combines both: m for the size class, K for the form/position class.
Size classes f/m/c/v
f (fine) for precision work and fine-mechanical parts. m (medium) by far the most common for general turning. c (coarse) for less critical parts. v (very coarse) for rough parts. Example 30–120 mm: f ±0.15 mm, m ±0.3 mm, c ±0.8 mm.
Form/position classes H/K/L
H is the finest, K middle (very common), L the coarsest class for flatness, straightness and squareness.
What about that -E? (envelope/Taylor)
A suffix -E or the envelope symbol means the Taylor condition applies: size and form are bounded together within the maximum-material envelope. Stricter, important for fits, and it can raise machining and inspection cost.
What this does to your price
Tighter tolerances cost money: sharper tooling, slower machining, more inspection and sometimes extra ops. The art is to tighten only where function demands and leave the rest on the general class.
Frequently asked questions
- What does ISO 2768-mK mean?
- Medium size class (m) combined with medium form/position class (K) — a common choice for general turning.
- Which class should I pick?
- For general turning, -m or -mK is enough. Use -f only where functionally required — tightening further raises cost without adding value.
- What is the tolerance on 50 mm under ISO 2768-m?
- ±0.3 mm. 50 mm falls in the range over 30 to 120 mm, where class m allows ±0.3 mm, so anything between 49.7 and 50.3 mm is in spec.
- Does ISO 2768 also cover angles and chamfers?
- Yes. ISO 2768-1 has separate tables for angles (based on the shorter leg) and for external radii and chamfer heights. Geometric tolerances such as flatness and perpendicularity are in ISO 2768-2 (classes H, K, L).