Choose single-part tolerance or shaft/hole fit.
Input the reference dimension in mm.
Provide upper and lower deviations (and hole deviations for fit mode).
See dimensional limits or fit classification.
Tolerance defines the range of acceptable dimensions for a manufactured part. Tighter tolerances cost more to manufacture but ensure better fit and function. The ISO 286 system uses standardized fit classifications: H7/g6 for free running fits, H7/n6 for transition, H7/p6 for press fits. Clearance fits have positive minimum clearance; interference fits have negative maximum clearance.
Max = Nominal + UpperDev • Min = Nominal + LowerDev • Tolerance = Max − Min
Tolerance under 0.01 mm: precision grinding/lapping required
Tolerance 0.01-0.05 mm: precision turning or milling
Tolerance 0.05-0.2 mm: standard machining capability
Tolerance 0.2-1 mm: typical of casting or rough machining
Tighter tolerances increase manufacturing cost exponentially
ISO 286 grades: IT01-IT4 precision, IT5-IT11 normal, IT12-IT18 coarse
Always specify only the tolerance you need — over-specifying wastes money
Tolerances define the acceptable range of variation in a manufactured dimension — the difference between a part that fits and one that must be scrapped. In mechanical engineering, tolerance is expressed as the difference between the maximum and minimum allowable dimension. For example, a shaft specified at 25.000 mm with a tolerance of ±0.025 mm must measure between 24.975 mm and 25.025 mm to pass inspection. The ISO 286 standard (also known as the IT grades system) defines 20 tolerance grades from IT01 (finest, about 0.3 micrometers for small parts) to IT18 (coarsest, several millimeters), giving engineers a standardized language for specifying precision. Tighter tolerances dramatically increase manufacturing cost — achieving IT6 precision (about 13 micrometers for a 25 mm dimension) typically requires grinding, while IT11 (about 130 micrometers) can be achieved with standard milling. Stack-up analysis, which calculates how individual part tolerances accumulate in an assembly, determines whether mating parts will fit correctly in the worst case. Whether you are designing a press-fit bearing housing, a sliding shaft, or a clearance hole for a bolt, selecting the right tolerance balances functional requirements against manufacturing feasibility and cost.
Engineering design is constantly trading manufacturing cost against functional requirements. Tighter tolerances guarantee better fit and performance but cost exponentially more. Loose tolerances are cheap but risk fit and function problems. The art of design is choosing the loosest tolerance that still meets the functional requirements — and no looser. This calculator helps you check the math both ways.
Data sourced from trusted institutions
All formulas verified against official standards.