Fit calculator

Our fit calculator is a quick and easy way to calculate the ideal tolerances and fits for your parts. The fit calculator is based on ISO 286, the international standard for tolerances and fits. 

Our fit calculator allows you to search for specific fit types, dimensions or tolerances and get quick results.

Note: The fit calculator has been tested. No errors were found, but we cannot guarantee the accuracy of the results. Also, the availability of the calculation is not guaranteed. Use at your own risk.

Fits and types of fits

For the manufacturing of CNC parts, the specification of the correct fits is very important. Fits describe the geometric relationship between two parts that fit together, for example a shaft and a bore. They determine how these parts interact with each other - whether they should move freely, fit exactly or be firmly connected.

Fits are critical in manufacturing and design because they define the functional relationships between mating parts. Fits enable engineers and designers to optimize the performance and service life of machinery and equipment.


Nominal dimension

The nominal dimension of a fit refers to the intended dimension of a part as specified in the technical drawings or design plans.

It serves as a reference point for tolerances and fits, the actual dimensions of the part deviate from the theoretical nominal dimension depending on the fit selected.

Tolerance degree

A tolerance degree is a value in manufacturing and design that defines the permissible deviation of a real dimension from the idealized nominal dimension.

The range is represented by the numbers 118. These numbers indicate the size of the tolerance zone, where 1 represents the narrowest and 18 the largest tolerance zone.

Tolerance position

Tolerance fields are identified by letters from A to ZC. The letters A to Z refer to bores. The lowercase letters a to zc refer to shafts. For bores, the tolerance field becomes wider as the letter increases. For shafts, the tolerance field becomes smaller as the letter increases.

Types of fits

Interference fit

An interference fit, also called a press fit, is a type of fit where the bore is smaller than the shaft that is pressed into it. This means the parts are brought together using pressure, for example.

Transition fit

In the transition fit, the tolerances of the shaft and bore are designed so that the diameter of the shaft is either slightly larger or smaller than the inner diameter of the bore. This ensures that the bore and shaft can be joined under light pressure.

Clearance fit

In a clearance fit, the inner diameter of the bore is always larger than the outer diameter of the shaft. This allows the mating parts to move.

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You are a contract manufacturer and want to make your business fit for the digital future? You want to calculate quote prices and manufacturing times for turning and milling parts more efficiently? With Spanflug Make  you can easily get started to digitize your quoting processes free of charge.