Engineering tool · ISO 286-1
Tolerance calculator.
Calculate the dimensional tolerance of a shaft or a hole according to ISO 286: select size, position, and grade to obtain maximum and minimum dimensions.
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Tolerance table: same position, other qualities
| Class | Upper deviation | Lower deviation | IT | Minimum dimension | Maximum dimension |
|---|
How to read an ISO tolerance: H7, h6, g6
A dimension like Ø25 H7 has three parts: the nominal size (25 mm), the position of the tolerance zone relative to the zero line (letter: uppercase for holes, lowercase for shafts) and the quality or tolerance grade (number: the lower, the more precise).
- H / h are the base positions: the H hole starts at the zero line and grows upwards; the h shaft starts at the zero line and goes down.
- A to G / a to g provide clearance (larger hole, smaller shaft). K to ZC / k to zc invade the zero line: transition or interference.
- At Proto&Go!, the reference for machining with a drawing is IT7 for metals and IT11 for engineering plastics. The team confirms the feasibility of the requested dimensions by reviewing the part.
What quality to request based on the process
| Proto&Go! process | Part with drawing | Example at Ø25 mm |
|---|---|---|
| CNC machining in metal | IT7 | H7 → from 25.000 to 25.021 mm |
| CNC machining in engineering plastics | IT11 | H11 → from 25.000 to 25.130 mm |
Dimensional, general, and geometric tolerances
This calculator covers the dimensional tolerances for shafts and holes per ISO 286. Dimensions without specified tolerances follow the general tolerances ISO 2768 (e.g., ISO 2768-mK), and form and position tolerances follow the geometric tolerances per ISO 1101.
What does H7 mean for a hole and what are its limit sizes?
H7 defines the size tolerance of a hole. The letter H fixes the lower deviation at zero: the minimum size matches the nominal. The grade 7 determines the tolerance range according to the diameter. For example, a Ø25 H7 hole accepts sizes between 25.000 and 25.021 mm.
What is the difference between H7 for a hole and h6 for a shaft?
Uppercase letters identify hole tolerances and lowercase letters identify shafts. In H7, the hole can be equal to or larger than the nominal size; in h6, the shaft can be equal to or smaller. For the same nominal diameter, the H7/h6 combination has a minimum clearance of zero. Grades 7 and 6 determine the range of each tolerance.
How do I calculate the maximum and minimum sizes for a shaft or hole according to ISO 286?
In the Proto&Go! tolerance calculator, select shaft or hole and enter the nominal size, position, and tolerance grade. You will obtain the maximum and minimum sizes in millimeters and the deviations in microns. The table allows comparing the available grades for that position. The tool covers nominal sizes greater than zero up to 500 mm.