ISO 286 Tolerance & Fit Calculator
Compute tolerance fields and fit ranges for any ISO 286 designation, and browse the full library of ISO 286-2 preferred fits with real clearance/interference numbers.
ISO 286 defines tolerances for linear dimensions using a letter (the "fundamental deviation", positioning the tolerance zone) plus a number (the "IT grade", sizing it) — for example H7 for a hole or g6 for a shaft. Combine a hole tolerance and a shaft tolerance at the same nominal diameter and you get a fit: clearance, transition, or interference, depending on how the two ranges compare.
The two calculators below compute this exactly as defined by ISO 286-1 (tolerance values) and ISO 286-2 (preferred fits) — the same dataset used inside the MechaHandbook app.
Tolerance Field Calculator
Pick a letter (uppercase = hole, lowercase = shaft) and an IT grade, e.g.
H + 7 for a hole reference, or g + 6 for a shaft.
Fit Calculator
Enter a hole and a shaft designation at the same nominal diameter to get the fit range.
ISO 286-2 Preferred Fits
Numbers below are computed at Ø 25 mm — change the diameter to recompute every card.
H11/c11
Wide fit
Large guaranteed clearance. Parts with wide freedom of movement, thermal expansion, dusty environments.
- Non-precision mating parts
- Fits with thermal expansion
- Agriculture, earthmoving
Clearance: +110 to +370 µm
H9/d9
Wide sliding fit
Medium clearance. Free sliding with lubrication. Medium-precision bearings.
- Plain bearings at high speed
- Sliding bushings
- Parts with frequent axial movement
Clearance: +65 to +169 µm
H8/f7
Sliding fit
Reduced clearance. Rotation and sliding with normal lubrication. One of the most common fits in general engineering.
- Rotating shafts on plain bearings
- Pins and pivots
- General couplings and bushings
Clearance: +20 to +74 µm
H7/g6
Precision sliding fit
Small clearance. Fine sliding with accurate positioning. Easy assembly and disassembly.
- Precision guides
- Hydraulic pistons
- Spindles on bearings
Clearance: +7 to +41 µm
H7/h6
Precision free fit
Minimum clearance. Part slides in by hand with no force. High-quality interchangeable fit.
- Frequently disassembled parts
- Instrumentation and metrology
- Centering without torque transmission
Clearance: 0 to +34 µm
H7/k6
Centering fit
Transition. Light clearance or interference. Excellent centering, removable with mallet. One of the most widely used fits.
- Gears on keyed shafts
- Pulleys and cranks
- Flange centering
Clearance +19 µm to interference +15 µm
H7/n6
Tight fit
Transition with prevailing interference. Removable with press. Good centering with no relative movement.
- Permanent bushings in housings
- Sealing rings
- Internal retaining rings
Clearance +6 µm to interference +28 µm
H7/p6
Light press fit
Guaranteed interference. Removable with press. Transmits small loads without a key.
- Cast iron or bronze bushings
- Rolling bearings on shafts
- Fixed pins
Interference: +1 to +35 µm
H7/s6
Press fit
Strong interference. Assembly by press or thermal method. Torque transmission without key.
- Wheels on railway axles
- Permanent sealing rings
- Gear rings on hubs
Interference: +14 to +48 µm
H7/u6
Heavy press fit
Very strong interference. Thermal assembly only. Permanent high-torque fit.
- Permanent high-torque shrink fits
- Heavy hubs on axles
Interference: +20 to +54 µm
C11/h11
Wide fit (shaft system)
Large guaranteed clearance. Shaft system.
- Parts with wide freedom of movement
- Harsh environments
Clearance: +110 to +370 µm
D9/h9
Wide sliding fit (shaft system)
Medium clearance. Free sliding with lubrication.
- Medium-precision bearings
- Sliding bushings
Clearance: +65 to +169 µm
F8/h7
Sliding fit (shaft system)
Reduced clearance. Rotation and sliding with normal lubrication.
- Rotating shafts on plain bearings
- Pins and pivots
Clearance: +20 to +74 µm
G7/h6
Precision sliding fit (shaft system)
Small clearance. Fine sliding with accurate positioning.
- Precision guides
- Hydraulic pistons
Clearance: +7 to +41 µm
H7/h6
Precision free fit (shaft system)
Minimum clearance. Identical to hole system — H7/h6 is common to both systems.
- Frequently disassembled parts
- Instrumentation
Clearance: 0 to +34 µm
K7/h6
Centering fit (shaft system)
Transition. Excellent centering, removable with mallet.
- Gears on keyed shafts
- Pulleys
Clearance +10 µm to interference +24 µm
N7/h6
Tight fit (shaft system)
Transition with prevailing interference.
- Permanent bushings
- Sealing rings
Interference: +2 to +36 µm
P7/h6
Light press fit (shaft system)
Guaranteed interference. Removable with press.
- Bronze bushings
- Rolling bearings
Interference: +9 to +43 µm
S7/h6
Press fit (shaft system)
Strong interference. Assembly by press or thermal method.
- Gear rings on hubs
- Permanent rings
IT Grade Reference Table (ISO 286-1)
Tolerance value in µm for each IT grade, by diameter class.
| Diameter (mm) | IT1 | IT2 | IT3 | IT4 | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 | IT12 | IT13 | IT14 | IT15 | IT16 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ≤ 3 | 0.8 | 1.2 | 2 | 3 | 4 | 6 | 10 | 14 | 25 | 40 | 60 | 100 | 140 | 250 | 400 | 600 |
| 3–6 | 1 | 1.5 | 2.5 | 4 | 5 | 8 | 12 | 18 | 30 | 48 | 75 | 120 | 180 | 300 | 480 | 750 |
| 6–10 | 1 | 1.5 | 2.5 | 4 | 6 | 9 | 15 | 22 | 36 | 58 | 90 | 150 | 220 | 360 | 580 | 900 |
| 10–18 | 1.2 | 2 | 3 | 5 | 8 | 11 | 18 | 27 | 43 | 70 | 110 | 180 | 270 | 430 | 700 | 1100 |
| 18–30 | 1.5 | 2.5 | 4 | 6 | 9 | 13 | 21 | 33 | 52 | 84 | 130 | 210 | 330 | 520 | 840 | 1300 |
| 30–50 | 1.5 | 2.5 | 4 | 7 | 11 | 16 | 25 | 39 | 62 | 100 | 160 | 250 | 390 | 620 | 1000 | 1600 |
| 50–80 | 2 | 3 | 5 | 8 | 13 | 19 | 30 | 46 | 74 | 120 | 190 | 300 | 460 | 740 | 1200 | 1900 |
| 80–120 | 2.5 | 4 | 6 | 10 | 15 | 22 | 35 | 54 | 87 | 140 | 220 | 350 | 540 | 870 | 1400 | 2200 |
| 120–180 | 3.5 | 5 | 8 | 12 | 18 | 25 | 40 | 63 | 100 | 160 | 250 | 400 | 630 | 1000 | 1600 | 2500 |
| 180–250 | 4.5 | 7 | 10 | 14 | 20 | 29 | 46 | 72 | 115 | 185 | 290 | 460 | 720 | 1150 | 1850 | 2900 |
| 250–315 | 6 | 8 | 12 | 16 | 23 | 32 | 52 | 81 | 130 | 210 | 320 | 520 | 810 | 1300 | 2100 | 3200 |
| 315–400 | 7 | 9 | 13 | 18 | 25 | 36 | 57 | 89 | 140 | 230 | 360 | 570 | 890 | 1400 | 2300 | 3600 |
| 400–500 | 8 | 10 | 15 | 20 | 27 | 40 | 63 | 97 | 155 | 250 | 400 | 630 | 970 | 1550 | 2500 | 4000 |
Values in micrometres (µm), from ISO 286-1:2010 Table 2. IT01 and IT0 omitted — metrology use only.
Glossary
- IT grade
- "International Tolerance" grade (IT1–IT16). Sets the width of the tolerance zone — lower numbers are tighter, higher numbers looser.
- Fundamental deviation
- The letter in a designation (e.g. the "g" in g6). Positions the tolerance zone relative to the nominal size.
- ES / EI
- Upper and lower deviation of a hole (uppercase letters), in µm from nominal.
- es / ei
- Upper and lower deviation of a shaft (lowercase letters), in µm from nominal.
- Hole-basis system
- Convention where the hole is always H (zero lower deviation) and the shaft letter is varied to obtain the desired fit. The most common approach in general engineering.
- Shaft-basis system
- Convention where the shaft is always h (zero upper deviation) and the hole letter is varied instead. Used when the shaft is a standard part (e.g. off-the-shelf round bar).
Frequently asked questions
What is ISO 286 and what are IT grades?
ISO 286 is the international standard defining tolerances for linear sizes. It splits the allowed variation into "IT grades" (IT1 to IT16) — the higher the number, the wider the allowed tolerance band. IT01 and IT0 exist for metrology use only and are omitted here since they are not used in general design.
What does a designation like "H7" or "g6" mean?
The letter is the "fundamental deviation" — it sets the position of the tolerance zone relative to the nominal size. Uppercase letters (A…ZC) are used for holes, lowercase (a…zc) for shafts. The number is the IT grade, which sets the width of that zone. So "H7" is a hole with zero lower deviation and IT grade 7, and "g6" is a shaft with a small negative deviation and IT grade 6.
What's the difference between the hole-basis and shaft-basis system?
Both are conventions for picking which of the two mating parts is held at a fixed tolerance so the other can be varied to get different fits. In the hole-basis system (the most common in practice) the hole is always H (zero lower deviation) and the shaft letter changes to get clearance, transition or interference. In the shaft-basis system it's the reverse: the shaft is always h (zero upper deviation) and the hole letter changes.
How do I read a fit like H7/g6 — is it clearance or interference?
Compute both tolerance fields at the nominal diameter, then compare their ranges: if the hole's minimum is always above the shaft's maximum, it's a clearance fit; if the hole's maximum is always below the shaft's minimum, it's an interference fit; if the ranges overlap, it's a transition fit (could be either depending on the actual manufactured sizes). The calculator above does this automatically.
What is a "preferred fit" and why use one?
ISO 286-2 recommends a shortlist of hole/shaft combinations — the "preferred fits" — that cover the vast majority of real design needs. Sticking to them means your tolerances match what tooling and gauges are commonly available for, instead of picking an arbitrary letter/grade combination that might be expensive or slow to manufacture and inspect.
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