An ISO tolerance calculator for shafts, holes and fits
This ISO tolerance calculator turns a nominal size and a fit such as H7/g6 into the actual limits of the hole and the shaft, then tells you whether the pair gives clearance, interference or a transition fit. Type any hole class (C to U) and shaft class (c to u) with grades IT5 to IT12, for sizes up to 500 mm, and the answer appears with a tolerance-zone diagram.
It follows the ISO system of limits and fits, ISO 286-1:2010, used across Europe and India (IS 919 is the Indian adoption) and mirrored by ANSI B4.2 for metric work in the US. Everything is calculated in your browser.
How to use the shaft and hole tolerance calculator
- Enter the nominal size in millimetres, the basic size written on the drawing (25 for Ø25).
- Pick a fit from the list of preferred fits, or type your own hole class and shaft class, for example H8 and f7.
- Read the clearance or interference range in the result, and the upper and lower deviations and size limits in the table.
- Check the zone diagram: the dashed zero line is the nominal size, the purple bar is the hole and the teal bar is the shaft.
- Press Copy limits to paste the result into a drawing note or inspection sheet.
ISO Fit Tolerance Calculator features
Any ISO class
Fourteen deviation letters for holes and shafts, grades 5–12, not just a few preset fits.
Clearance or interference
Maximum and minimum clearance, fit tolerance and mean, labelled as clearance, transition or interference.
ISO rules, not guesses
Hole deviations come from the shaft deviations by the ISO Δ rule, including the M6 special case.
Zone diagram
An SVG drawing of both zones against the zero line, redrawn as you type.
Preferred fits
The ten hole-basis and nine shaft-basis preferred fits from loose running to force fit.
How ISO limits and fits are calculated
A class such as g6 has two parts. The letter sets the fundamental deviation, the limit nearest the nominal size; the number is the IT grade, the width of the zone. For a 25 mm shaft, g has an upper deviation of −7 µm and IT6 is 13 µm, so g6 runs from −0.007 to −0.020 mm: 24.993 to 24.980 mm. H7 for the hole starts at zero and is 21 µm wide, 25.000 to 25.021 mm.
Minimum clearance is the smallest hole minus the largest shaft, here 0.007 mm; maximum clearance is the largest hole minus the smallest shaft, 0.041 mm. When both are positive it is a clearance fit, when both are negative an interference fit, and otherwise a transition fit.
The tolerance widths come from the standard tolerance factor i = 0.45·∛D + 0.001·D µm, where D is the geometric mean of the size step (for 18–30 mm, D = 23.24 and i = 1.31 µm), multiplied by 10 for IT6, 16 for IT7, 25 for IT8 and 40 for IT9. The published values are rounded and, for a few steps, adjusted (6–10 mm IT7 is 15 µm, not the 14.4 µm the formula gives), so the calculator uses the standard values and shows i only for reference.
Preferred fits at a glance (Ø25 mm)
| Fit | Type | Typical use | Clearance (µm) |
|---|---|---|---|
| H11/c11 | Clearance | Loose running, wide tolerances | +110 to +370 |
| H9/d9 | Clearance | Free running, high speed | +65 to +169 |
| H8/f7 | Clearance | Close running on machine tools | +20 to +74 |
| H7/g6 | Clearance | Sliding, precise location | +7 to +41 |
| H7/h6 | Clearance | Locational, assembled by hand | 0 to +34 |
| H7/k6 | Transition | Accurate location, light press | −15 to +19 |
| H7/p6 | Interference | Locational press fit | −35 to −1 |
| H7/s6 | Interference | Medium drive fit | −48 to −14 |
Limits of this calculator
- Covers sizes over 0 up to 500 mm, grades IT5–IT12 and the letters c–u; the rarely used a, b, cd, ef, fg, j, t and v–zc are left out.
- Values are the ISO 286 tables, cross-checked against two published references; check the standard and your drawing before making parts.
- Interference fits need a stress and assembly-force check, and temperature changes the fit — steel grows about 11.5 µm per metre per °C.
ISO Fit Tolerance Calculator FAQ
What is the tolerance of H7/g6 for a 25 mm shaft?
The hole H7 is +0.021/0 mm (25.000 to 25.021) and the shaft g6 is −0.007/−0.020 mm (24.980 to 24.993). The fit always has clearance, between 0.007 and 0.041 mm.
How do I use this tolerance calculator for a shaft only?
Enter the size and type the shaft class, e.g. h6 or k6; the shaft row of the table gives its limits whatever hole you choose.
What is the difference between hole basis and shaft basis?
Hole basis keeps the hole at H and changes the shaft letter to get different fits, which suits reamed holes and standard gauges. Shaft basis keeps the shaft at h, useful for bright-drawn bar or one shaft carrying several parts.
Which fit should I use for a press fit?
H7/p6 is a light locational press fit and H7/s6 a medium drive fit for steel parts; H7/u6 is a force fit. Check hub stresses and assembly force before choosing.
Is H7/k6 a clearance or interference fit?
A transition fit: for Ø25 it can range from 0.019 mm clearance to 0.015 mm interference, so parts may need light pressure to assemble.
Does this follow ISO 286-2 tables exactly?
Yes for the classes covered: the standard tolerances and fundamental deviations are those of ISO 286-1, hole values are derived with its rules, and spot values agree with published ISO 286-2 tables. Use the standard itself for contractual work.