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ISO Tolerance Calculator (IT Grades)
Enter nominal size and IT grade — tolerance band appears instantly.
Formula
i = 0.45·∛D + 0.001·D | ITn = a·i (a: IT5=7, IT6=10, IT7=16, IT8=25, IT9=40, IT10=64, IT11=100, IT12=160)
Typical Usage
| Grade | Typical use |
|---|---|
| IT5–IT6 | Precision bearings, gauges |
| IT7 | General machine fits (H7/g6) |
| IT8–IT9 | Machined non-critical parts |
| IT11–IT12 | Drilled / rough-machined |
FAQ
How does the calculator handle size ranges?
ISO defines i using the geometric mean of each size band. This calculator uses the nominal size directly — accurate to a few percent, ideal for quick checks.
What does IT7 mean for a 25 mm hole?
i ≈ 1.31 µm, IT7 = 16i ≈ 21 µm — the hole may be 0 to +0.021 mm over nominal. (H7 for 18–30: exact value +21 µm ✓)