Fits & tolerances calculator
Pick a diameter and a fit, get the hole and shaft limits and the actual clearance or interference in millimetres. Hole-basis system, nominal sizes up to 500 mm.
Choosing the right fit
| Fit | Name | Type | Typical use |
|---|---|---|---|
| H11/c11 | Loose running | Clearance | Wide tolerance, dirty environments, agricultural machinery, thermal movement. |
| H9/d9 | Free running | Clearance | Large clearance, high temperature, long engagement lengths, sleeve bearings. |
| H8/f7 | Close running | Clearance | Accurate location with free running under lubrication — pumps, gearbox shafts. |
| H7/g6 | Sliding | Clearance | Parts that must slide or index freely but locate accurately. Very common. |
| H7/h6 | Locational clearance | Clearance | Assembles and disassembles by hand; free but with no perceptible play. |
| H7/k6 | Locational transition | Transition | Accurate location with slight interference — gear on shaft, keyed hubs. |
| H7/n6 | Tight transition | Transition | Firmer location, needs light press. Bearings on housing seats. |
| H7/p6 | Light press | Interference | Permanent-ish assembly, press or thermal fit. Bushings, dowel pins. |
| H7/s6 | Medium press | Interference | Heavy interference for torque transmission in steel; thermal fitting recommended. |
IT tolerance grades (µm)
The IT grade sets only the width of the tolerance band. IT6–IT7 is normal machining practice, IT8–IT10 covers general turning and milling, IT11+ is casting and flame-cut work.
| Size (mm) | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 | IT12 | IT13 |
|---|---|---|---|---|---|---|---|---|---|
| 0–3 | 4 | 6 | 10 | 14 | 25 | 40 | 60 | 100 | 140 |
| 3–6 | 5 | 8 | 12 | 18 | 30 | 48 | 75 | 120 | 180 |
| 6–10 | 6 | 9 | 15 | 22 | 36 | 58 | 90 | 150 | 220 |
| 10–18 | 8 | 11 | 18 | 27 | 43 | 70 | 110 | 180 | 270 |
| 18–30 | 9 | 13 | 21 | 33 | 52 | 84 | 130 | 210 | 330 |
| 30–50 | 11 | 16 | 25 | 39 | 62 | 100 | 160 | 250 | 390 |
| 50–80 | 13 | 19 | 30 | 46 | 74 | 120 | 190 | 300 | 460 |
| 80–120 | 15 | 22 | 35 | 54 | 87 | 140 | 220 | 350 | 540 |
| 120–180 | 18 | 25 | 40 | 63 | 100 | 160 | 250 | 400 | 630 |
| 180–250 | 20 | 29 | 46 | 72 | 115 | 185 | 290 | 460 | 720 |
| 250–315 | 23 | 32 | 52 | 81 | 130 | 210 | 320 | 520 | 810 |
| 315–400 | 25 | 36 | 57 | 89 | 140 | 230 | 360 | 570 | 890 |
| 400–500 | 27 | 40 | 63 | 97 | 155 | 250 | 400 | 630 | 970 |
Frequently asked
What does H7/g6 mean?
H7 is the hole: its lower limit is exactly the nominal size and its upper limit is nominal plus the IT7 tolerance. g6 is the shaft: it sits slightly below nominal with an IT6 tolerance band. The result is a small guaranteed clearance — a precision sliding fit.
What is the difference between hole-basis and shaft-basis fits?
In hole-basis (the ISO default) the hole is always H and the fit is changed by selecting the shaft letter. In shaft-basis the shaft is always h and the hole letter varies. Hole-basis is preferred because reamers and standard tooling fix hole sizes more cheaply than turning fixes shaft sizes.
Which fit should I use for a ball bearing on a shaft?
For a rotating inner ring under normal load, k6 or m6 on the shaft and H7 in the housing is the usual starting point. Always check the bearing manufacturer's shaft and housing tolerance tables, because the correct fit depends on load direction and whether the inner or outer ring rotates.
What is an IT grade?
IT stands for International Tolerance grade. It defines only the width of the tolerance band, not its position: IT7 at 25 mm is 21 µm wide. The letter (H, g, p ...) positions that band relative to nominal size.
Values follow ISO 286-1/-2 for nominal sizes to 500 mm. Shaft letters c, d, f, g, h, k, n and p are supported; for s, u and beyond, check the full standard because the deviation steps in finer size bands.
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