Calculate tolerances
Deviations and fits per ISO 286. Enter the nominal size and tolerance class, get exact limits in µm and mm.
- Upper deviation
- -
- Lower deviation
- -
- Maximum size
- -
- Minimum size
- -
- Tolerance IT
- -
- Upper deviation
- -
- Lower deviation
- -
- Maximum size
- -
- Minimum size
- -
- Tolerance IT
- -
IT standard tolerances per ISO 286
Standard tolerances in µm per nominal size range. The columns show grades IT5 to IT12, the ones commonly used in machining.
| Nominal size (mm) | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 | IT12 |
|---|---|---|---|---|---|---|---|---|
| over 0 to 3 | 4 | 6 | 10 | 14 | 25 | 40 | 60 | 100 |
| over 3 to 6 | 5 | 8 | 12 | 18 | 30 | 48 | 75 | 120 |
| over 6 to 10 | 6 | 9 | 15 | 22 | 36 | 58 | 90 | 150 |
| over 10 to 18 | 8 | 11 | 18 | 27 | 43 | 70 | 110 | 180 |
| over 18 to 30 | 9 | 13 | 21 | 33 | 52 | 84 | 130 | 210 |
| over 30 to 50 | 11 | 16 | 25 | 39 | 62 | 100 | 160 | 250 |
| over 50 to 80 | 13 | 19 | 30 | 46 | 74 | 120 | 190 | 300 |
| over 80 to 120 | 15 | 22 | 35 | 54 | 87 | 140 | 220 | 350 |
| over 120 to 180 | 18 | 25 | 40 | 63 | 100 | 160 | 250 | 400 |
| over 180 to 250 | 20 | 29 | 46 | 72 | 115 | 185 | 290 | 460 |
| over 250 to 315 | 23 | 32 | 52 | 81 | 130 | 210 | 320 | 520 |
| over 315 to 400 | 25 | 36 | 57 | 89 | 140 | 230 | 360 | 570 |
| over 400 to 500 | 27 | 40 | 63 | 97 | 155 | 250 | 400 | 630 |
How the ISO tolerance system works
A tolerance callout such as Ø30 H7 has two parts. The letter defines the position of the tolerance zone relative to the zero line, the number defines the IT grade and therefore the width of the zone.
Capital letters denote holes, lowercase letters denote shafts. H means the lower deviation sits exactly on the nominal size, so the hole can only be larger. h is the shaft counterpart, it can only be smaller.
German mechanical engineering predominantly uses the hole-basis system: the hole stays H and the fit is set through the shaft. This saves tooling, because reamers and plug gauges only need to be stocked in H.
Scope of this calculator: Holes D to H plus JS, shafts d to p plus js. This covers clearance, transition and light interference fits. For heavy interference fits (r, s, u) please contact us; their fundamental deviations are further subdivided in the standard.
What tolerances cost
Every tighter IT grade costs machining time and inspection effort. The design rule of thumb: tolerance tightly where function demands it, otherwise ISO 2768-m.
Normal CNC machining with no extra effort. The baseline for costing.
Additional finishing pass, closer tool monitoring. Around 15 to 30% extra cost.
Fine finishing, temperature-controlled measurement, 100% inspection. Around 40 to 80% extra cost.
Not reliably achievable by turning and milling alone. Grinding as an additional operation.
Strobel Industry produces from IT6 as standard. Tighter tolerances are realised through grinding within our partner network. Send us the drawing and we will check feasibility within 24 hours.
Frequently asked questions
What does H7 mean?
H7 is a tolerance callout for a hole. The H specifies that the lower deviation sits exactly on the nominal size, so the hole is never smaller than nominal. The 7 is the IT grade, which sets the width of the tolerance zone. At Ø30 H7 that width is 21 µm, so the hole may measure between 30.000 and 30.021 mm.
What is the tolerance for Ø30 H7?
Ø30 H7 has an upper deviation of +21 µm and a lower deviation of 0. The maximum size is 30.021 mm and the minimum size is exactly 30.000 mm. The IT7 standard tolerance in this size range is 21 µm.
What is the difference between H7 and h7?
Capital letters denote holes, lowercase letters denote shafts. H7 is a hole that may only be larger than nominal. h7 is a shaft that may only be smaller. The width of the tolerance zone is the same for both, only its position relative to the zero line is mirrored.
What are clearance, transition and interference fits?
In a clearance fit the shaft is always smaller than the hole and the parts assemble freely (e.g. H7/g6). In a transition fit there may be either clearance or interference depending on the actual sizes (e.g. H7/k6). In an interference fit the shaft is always larger, so assembly requires force or a temperature difference (e.g. H7/p6).
Which tolerances are achievable in CNC turning and milling?
We achieve IT6 as standard. IT7 and IT8 are routine and cause moderate additional effort. IT5 and finer cannot be reliably held by turning and milling alone; that requires grinding as an additional operation.
What does ISO 2768-m mean?
ISO 2768 governs general tolerances for dimensions without an individually stated tolerance. Class m (medium) is the usual standard in machining and corresponds roughly to IT12 to IT14 depending on the nominal size. Tolerancing tightly only where function demands it and leaving the rest at ISO 2768-m saves considerable inspection and machining time.
Why does a tighter tolerance cost more?
Tight tolerances require additional finishing passes, slower cutting data, more frequent tool changes and closer inspection. From IT6 onwards, temperature-controlled measurement and often 100% inspection are added. Going from IT9 to IT6 raises cost by 40 to 80% depending on the part.
Request a part
Send us a drawing or 3D model. We check the required tolerances for feasibility and quote within 24 hours.
Start inquiry