ISO Fits and Tolerances Calculator
Enter a nominal size and an ISO 286 fit such as H7/g6 or H7/p6 to get the upper and lower limits of the hole and the shaft, the maximum and minimum clearance or interference, and whether it is a clearance, transition or interference fit. Works with any hole or shaft zone from c to u and IT1 to IT13, for sizes up to 500 mm.
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e.g. H7/g6, H7/p6, H8/f7, G7/h6. Hole letter is uppercase, shaft lowercase. Or just one zone: H7 or k6.
How to use the ISO Fits and Tolerances Calculator
- Enter the nominal size of the hole and shaft, in mm or inches.
- Type the fit, hole zone first in capitals and shaft zone in lowercase, e.g. H7/g6, or tap a preset.
- Read the fit type and the max and min clearance or interference.
- Check the limits of the hole and the shaft to put on your drawing or to set up machining.
- Compare preferred fits in the table to pick a tighter or looser one.
How ISO 286 fits work
An ISO tolerance zone is written as a letter and a number. The letter (the fundamental deviation) sets how far the zone sits from the nominal size; capitals are holes, lowercase are shafts. The number is the international tolerance grade (IT), which sets the width of the zone and grows with size. A fit combines a hole zone and a shaft zone, for example H7/g6.
- Hole-basis system (H holes): the hole has lower deviation 0 and the shaft letter changes the fit. It is the most common because standard reamers and plug gauges fit H holes.
- Shaft-basis system (h shafts): the shaft stays at h and the hole letter varies, used for long ground shafts carrying several parts.
- Shafts a to h are below the nominal size (clearance), js is symmetric, and k to zc are above it (transition and interference with an H hole).
IT tolerance grades (µm)
| Size over–to (mm) | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 |
|---|---|---|---|---|---|---|---|
| 0–3 | 4 | 6 | 10 | 14 | 25 | 40 | 60 |
| 3–6 | 5 | 8 | 12 | 18 | 30 | 48 | 75 |
| 6–10 | 6 | 9 | 15 | 22 | 36 | 58 | 90 |
| 10–18 | 8 | 11 | 18 | 27 | 43 | 70 | 110 |
| 18–30 | 9 | 13 | 21 | 33 | 52 | 84 | 130 |
| 30–50 | 11 | 16 | 25 | 39 | 62 | 100 | 160 |
| 50–80 | 13 | 19 | 30 | 46 | 74 | 120 | 190 |
| 80–120 | 15 | 22 | 35 | 54 | 87 | 140 | 220 |
| 120–180 | 18 | 25 | 40 | 63 | 100 | 160 | 250 |
| 180–250 | 20 | 29 | 46 | 72 | 115 | 185 | 290 |
| 250–315 | 23 | 32 | 52 | 81 | 130 | 210 | 320 |
| 315–400 | 25 | 36 | 57 | 89 | 140 | 230 | 360 |
| 400–500 | 27 | 40 | 63 | 97 | 155 | 250 | 400 |
A size exactly on a boundary (for example 30 mm) belongs to the lower range ("over 18 up to and including 30").
Choosing a fit
| Fit | Type | Typical use |
|---|---|---|
| H11/c11 | Loose running | Wide commercial tolerances, parts exposed to dirt or heat |
| H9/d9 | Free running | Large temperature changes, high speeds, heavy journal pressure |
| H8/f7 | Close running | Accurate running on machine tools, moderate speeds |
| H7/g6 | Sliding | Parts that move and turn freely but locate accurately (gears on splines, pistons) |
| H7/h6 | Locational clearance | Snug fit for stationary parts that can be assembled by hand |
| H7/k6 | Locational transition | Accurate location, compromise between clearance and interference |
| H7/n6 | Locational transition | More accurate location where greater interference is allowed |
| H7/p6 | Locational interference | Rigid location with light press; parts can be dismantled |
| H7/s6 | Medium drive | Ordinary steel parts, shrink fits on light sections |
| H7/u6 | Force | Highly stressed parts, or shrink fits where heavy pressing is impractical |
Interference fits also depend on materials, wall thickness and temperature; check the resulting pressure and stresses for critical assemblies.
Frequently asked questions
What does H7/g6 mean?
It is an ISO 286 hole-basis fit. H7 is the hole: fundamental deviation H (lower limit at the nominal size) with tolerance grade IT7. g6 is the shaft: deviation g (slightly below nominal) with grade IT6. At 25 mm the hole is 25.000 to 25.021 mm and the shaft 24.980 to 24.993 mm, giving 7 to 41 µm of clearance: a precise sliding fit.
What is the tolerance of H7?
The H7 hole has a lower deviation of 0 and an upper deviation equal to the IT7 value, which depends on size: +12 µm for 3–6 mm, +15 µm for 6–10 mm, +18 µm for 10–18 mm, +21 µm for 18–30 mm, +25 µm for 30–50 mm and +30 µm for 50–80 mm.
What is the difference between clearance, transition and interference fits?
In a clearance fit the smallest hole is always bigger than the largest shaft, so there is always play. In an interference fit the shaft is always bigger and must be pressed or shrunk in. A transition fit can end up either way depending on the actual sizes, giving accurate location with light assembly force.
Which fit should I use for a bearing or a press-fit pin?
Rolling bearing seats often use k5/k6 or m6 shafts for rotating inner rings and H7 or J7 housings. Dowel pins in holes for accurate location commonly use H7/m6 or H7/n6, while permanent press fits such as bushings use H7/p6 or H7/s6. Always follow the bearing or component maker's recommendation.
How are the clearance and interference calculated?
Maximum clearance = largest hole − smallest shaft = ES − ei. Minimum clearance = smallest hole − largest shaft = EI − es. A negative minimum clearance means interference. The fit tolerance (the spread of the fit) equals the hole tolerance plus the shaft tolerance.
What sizes and zones does the calculator cover?
Nominal sizes from just above 0 up to 500 mm, tolerance grades IT1 to IT13, and the deviations c to u most used in practice, including js/JS. Values follow the ISO 286-1 and 286-2 tables, including the Δ correction for K, M, N and P to U holes.
Can I use inch sizes?
Yes. Inch sizes are converted to millimetres to choose the ISO size range, and results can be shown in inches. For North American designs specified in inches, the ANSI B4.1 preferred fits (RC, LC, LT, LN, FN classes) are a separate system with different values.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.