ISO 286 calculator: hole, shaft and what is left after the machine
Set a size, a hole H and a shaft and get the deviations, the limit sizes and the clearance or interference, plus a comparison with the spread of the machine. The calculation runs in your browser.
Opens without an account 3 times a day. A free account removes the limit.
- 12 size bandsfrom 3 to 500 mm
- 9 lettersfor the shaft, e to p
- up to 441fits tried for a clearance
- 4 processesFDM, SLA, SLS/MJF, CNC
What tolerances and fits (ISO 286) mean
This ISO 286 calculator from EduFacturing is a free online tool that works out, for a hole and a shaft in the hole-basis system, the deviations, the clearance or interference and the kind of fit. Sizes run from over 3 to 500 mm.
The tool also says what is left after a machine: for ⌀25 H7/g6, FDM at ±0.15 mm is 8.8 times coarser than the fit.
ISO 286 fit calculator: deviations, limit sizes, clearance
Calculates a fit to ISO 286
Hole H5 to H11, shaft e, f, g, h, js, k, m, n or p in IT5 to IT11. It gives deviations, limit sizes, clearance or interference and the kind of fit. Eight preferred fits are one click away.
Searches for a fit by clearance
The reverse problem tries up to 441 combinations and shows the first 12 by a score (coverage of the clearance you ask for, offset, spill outside it). A negative value is interference.
Handles chains, temperature and measurements
Chain: worst case and statistical. Temperature: how the fit changes, for 11 materials. Measured: whether the part passes.
Checks the fit against the machine
The span is compared with the spread of FDM, SLA, SLS/MJF or CNC; if the process cannot hold the fit, a clearance is recommended (for FDM).
When to use a fit calculator
A fit is chosen for its function, then checked for whether the machine can hold it.
Shaft and bore
H7/g6 for rotation, H7/h6 for sliding, H7/k6 for location and H7/p6 for interference, with the limit sizes for the drawing.
3D printing
When the process cannot hold the fit, you get a functional clearance for a tight, sliding and free joint.
How the deviations and the fit type are worked out
The size picks a band, the band and the letter give the deviations, and the fit follows.
Size band
The size falls in one of 12 bands. ISO works with the geometric mean D of the band.
Deviations
IT comes from the ISO 286-1 table: IT7 is 21 µm at 18 to 30 mm. The shaft's fundamental deviation is a formula by letter, for p a table.
The fit
The hole is H: its smallest size is the nominal. Clearance is hole minus shaft: if the minimum is not negative it is a clearance fit, if the maximum is not positive interference, otherwise transition.
The machine
The span is compared with 2·(±process). If the process is coarser, the tool says by how many times and recommends a clearance.
| Applies to | Formula | Meaning |
|---|---|---|
| Shaft e, f, g | e = −11·D^0.41; f = −5.5·D^0.41; g = −2.5·D^0.34 | upper deviation es in µm, rounded to a whole number; ei = es − IT |
| Shaft k, m, n | k = +0.6·∛D; m = IT7 − IT6; n = +5·D^0.34 | lower deviation ei; k applies for IT4 to IT7, otherwise 0 |
| Clearance | max = ES − ei; min = EI − es | interference is negative clearance; span = max − min |
| Chain and temperature | worst = Σ|t|; RSS = √(Σt²); Δd = d·α·ΔT | α is 11.7·10⁻⁶ for steel and 23.1·10⁻⁶ for aluminium; ΔT is the same for both parts |
Reference
ISO 286 hole and shaft deviations (µm) by size range
| Parameter | Value | Unit |
|---|---|---|
| H7 3-6 mm | 0 .. 12 | µm |
| H7 6-10 mm | 0 .. 15 | µm |
| H7 10-18 mm | 0 .. 18 | µm |
| H7 18-30 mm | 0 .. 21 | µm |
| H7 30-50 mm | 0 .. 25 | µm |
| H7 50-80 mm | 0 .. 30 | µm |
| H7 80-120 mm | 0 .. 35 | µm |
| H7 120-180 mm | 0 .. 40 | µm |
| g6 3-6 mm | -12 .. -4 | µm |
| g6 6-10 mm | -14 .. -5 | µm |
| g6 10-18 mm | -17 .. -6 | µm |
| g6 18-30 mm | -20 .. -7 | µm |
| g6 30-50 mm | -25 .. -9 | µm |
| g6 50-80 mm | -29 .. -10 | µm |
| g6 80-120 mm | -34 .. -12 | µm |
| g6 120-180 mm | -39 .. -14 | µm |
| h6 3-6 mm | -8 .. 0 | µm |
| h6 6-10 mm | -9 .. 0 | µm |
| h6 10-18 mm | -11 .. 0 | µm |
| h6 18-30 mm | -13 .. 0 | µm |
| h6 30-50 mm | -16 .. 0 | µm |
| h6 50-80 mm | -19 .. 0 | µm |
| h6 80-120 mm | -22 .. 0 | µm |
| h6 120-180 mm | -25 .. 0 | µm |
| k6 3-6 mm | 1 .. 9 | µm |
| k6 6-10 mm | 1 .. 10 | µm |
| k6 10-18 mm | 1 .. 12 | µm |
| k6 18-30 mm | 2 .. 15 | µm |
| k6 30-50 mm | 2 .. 18 | µm |
| k6 50-80 mm | 2 .. 21 | µm |
| k6 80-120 mm | 3 .. 25 | µm |
| k6 120-180 mm | 3 .. 28 | µm |
| p6 3-6 mm | 12 .. 20 | µm |
| p6 6-10 mm | 15 .. 24 | µm |
| p6 10-18 mm | 18 .. 29 | µm |
| p6 18-30 mm | 22 .. 35 | µm |
| p6 30-50 mm | 26 .. 42 | µm |
| p6 50-80 mm | 32 .. 51 | µm |
| p6 80-120 mm | 37 .. 59 | µm |
| p6 120-180 mm | 43 .. 68 | µm |
Actual size = nominal + deviation/1000. H7 is a hole; g6, h6, k6, p6 are shafts, typically paired with H7.
A fit checked against the machine
Shows how many times coarser the process is
At ⌀25 H7/g6 the span is 34 µm: FDM is 8.8 times coarser, SLS 5.9, SLA 2.9 and even CNC at ±0.02 mm 1.2 times.
Shows when temperature changes the kind
An H7/p6 at ⌀25 with an aluminium hub on a steel shaft becomes a transition fit already at a +4 °C difference.
Hole-basis only (H) and metric ISO 286. Letters a to d and r to zc are missing because there are no two independent verified sources (for c and d the formula departs from the tables), and p has verified values only for 3 to 180 mm.
Temperature applies equally to both parts, heating only one is not calculated. The expansion coefficients for PLA, PETG, ABS and nylon are indicative. The statistical chain holds only for mass production centred on the nominal.
Questions about H7 and fits
What is H7 tolerance, and what are the limits of ⌀25 H7/g6?
H7 is a hole in the hole-basis system: its smallest size is the nominal, and IT7 is 21 µm at 18 to 30 mm. Hole H7: 25.000 to 25.021 mm (0 to +21 µm). Shaft g6: 24.980 to 24.993 mm (−20 to −7 µm). The clearance is 7 to 41 µm and the span is 34 µm: a clearance fit.
What is a fit, and how do H7/h6, H7/k6 and H7/p6 differ at ⌀25?
A fit is how a hole and a shaft go together. H7/h6 is a clearance fit, 0 to 34 µm. H7/k6 is a transition fit, −15 to +19 µm. H7/p6 is an interference fit, 1 to 35 µm.
How much does temperature change a fit?
At ⌀25, with an aluminium hole, a steel shaft and a +60 °C difference (from 20 °C), the clearance grows 17.1 µm. For H7/p6 the interference disappears at about a +123 °C difference, if both parts are equally warm.
Why is H7/g6 not suited to FDM printing?
H7/g6 at ⌀25 has a span of 34 µm, while FDM is ±0.15 mm, or 300 µm. When the process cannot hold the fit, the tool recommends a clearance: 0.10 to 0.20 mm for an interference fit, 0.20 to 0.35 for a transition fit and 0.35 to 0.50 for a clearance fit. FDM does hold a wide fit such as H11/h11 at ⌀100.
How do tolerances stack in a chain?
Worst case adds all the ± values, the statistical one is the square root of the sum of squares. For 100 ±0.1, −40 ±0.05 and −2 ±0.02 mm they are ±0.17 and ±0.114 mm: 1.5 times tighter.
Is the ISO 286 calculator free, and do I need an account?
Yes, it is free. Without an account it opens 3 times a day. A free account removes the limit.
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