What is an engineering tolerance calculator?

An engineering tolerance calculator computes the allowable dimensional limits (max and min) for a part given its nominal size and deviation. It can also determine the type of fit (clearance, transition, or interference) when matching a shaft to a hole.

What is the difference between clearance, transition, and interference fits?

Clearance fit: shaft is always smaller than hole — free running. Transition fit: could be either depending on actual sizes — used for locating but not retaining. Interference fit: shaft always larger than hole — press fits, requires force assembly.

How is tolerance width calculated?

Tolerance width = Maximum Limit − Minimum Limit = Upper Deviation − Lower Deviation. Example: 25 +0.021 / 0 has a tolerance width of 0.021 mm.

What does ISO 286 specify?

ISO 286 is the international standard for limits and fits. It defines tolerance grades (IT01-IT18) and fundamental deviations (a-zc for shafts, A-ZC for holes). Common fits like H7/g6 use this notation to specify both parts simultaneously.

Why does tolerance affect cost?

Tighter tolerances require more precise machining, more inspection, more rework on out-of-spec parts, and often more expensive equipment. Cost increases roughly exponentially as tolerance tightens. Over-specifying tolerance is one of the most common ways to waste money in manufacturing.

Tolerance Calculator

Engineering tolerance is the allowable variation in a manufactured dimension. Our tolerance calculator handles two common cases: single-part tolerance (nominal ± deviations gives max and min limits) and shaft/hole fit calculation (combining hole and shaft tolerances to determine whether the resulting fit is clearance, transition, or interference). Both modes return all the relevant dimensional limits plus an interpretation of what the tolerance width implies for manufacturing process choice.

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calendar_today Updated: April 2026

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straightenDimensions (mm)

Mode

Nominal Size

Upper Dev (shaft)

Lower Dev (shaft)

analyticsLimits

Max Limit

25.021

Min Limit

25.000

Tolerance Width

0.021

Mid Limit

25.0105

Interpretation

Tight tolerance — precision turning or milling

Input Values

Mode

Single Part

Shaft/Hole Fit

Nominal Size (mm)

Upper Deviation (mm)

Lower Deviation (mm)

Hole Upper Dev (fit mode)

Hole Lower Dev (fit mode)

tips_and_updates Tips

• 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

functions Formula

{Max = Nominal + UpperDev • Min = Nominal + LowerDev • Tolerance = Max − Min [{Nominal Reference dimension} {Upper Dev. Positive deviation from nominal} {Lower Dev. Negative deviation from nominal} {Tolerance Width Max − Min — total allowable range} {Max Clearance Hole Max − Shaft Min (positive in clearance fit)} {Min Clearance Hole Min − Shaft Max (positive in clearance fit)}] 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.}

science Example: 25 mm shaft, +0.021/0 deviation

Maximum size 25.021 mm, minimum 25.000 mm, tolerance width 0.021 mm (21 µm). Falls in the tight tolerance range — needs precision turning or grinding to achieve.

Expected Results

Max Limit 25.0

Min Limit 25

Tolerance Width 0.0

Mid Limit 25.0

How to Use This Calculator

Pick mode

Choose single-part tolerance or shaft/hole fit.

Enter nominal size

Input the reference dimension in mm.

Enter deviations

Provide upper and lower deviations (and hole deviations for fit mode).

Read result

See dimensional limits or fit classification.

The Formula

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

lightbulb Variables Explained

Nominal Reference dimension
Upper Dev. Positive deviation from nominal
Lower Dev. Negative deviation from nominal
Tolerance Width Max − Min — total allowable range
Max Clearance Hole Max − Shaft Min (positive in clearance fit)
Min Clearance Hole Min − Shaft Max (positive in clearance fit)

tips_and_updates Pro Tips

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

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.

Frequently Asked Questions

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