Engineering Fits Calculator

ISO 286 tolerance calculator for hole-basis fits. Calculate clearance, transition, and interference fits with a tolerance-zone diagram.

Inputs

Mode

Fit Type

Common Fit

Nominal Diameter (mm)

Basic size D (1–500 mm)

Select a fit and enter dimensions, then click Calculate.

Tolerance Zone Diagram

Hole and shaft tolerance zones shown as deviations from the nominal (zero) line.

Calculate a fit to see its tolerance zones.

Deviation Symbols (ISO 286)

A deviation is the signed distance from the nominal (basic) size to a limit. UPPERCASE = hole, lowercase = shaft:

ES	Hole upper deviation — nominal → largest hole (écart supérieur)
EI	Hole lower deviation — nominal → smallest hole (écart inférieur)
es	Shaft upper deviation — nominal → largest shaft
ei	Shaft lower deviation — nominal → smallest shaft

The gap between the two deviations is the tolerance (IT grade). For hole basis, the hole's lower deviation EI = 0, so the hole starts exactly at nominal.

ISO 286 Tolerance Calculations

The ISO system uses a standard tolerance unit i that scales with diameter:

\[ i = 0.45 \cdot D^{1/3} + 0.001 \cdot D \quad \text{(μm)} \]

IT grade tolerances are multiples of this unit:

\[ IT_n = k_n \cdot i \]

Where \(k_n\) is the grade multiplier (e.g., IT7 = 16i, IT6 = 10i)

Size Limits

\[ D_{hole,max} = D + ES \quad,\quad D_{hole,min} = D + EI \] \[ D_{shaft,max} = D + es \quad,\quad D_{shaft,min} = D + ei \]

Clearance / Interference

\[ C_{min} = D_{hole,min} - D_{shaft,max} = EI - es \] \[ C_{max} = D_{hole,max} - D_{shaft,min} = ES - ei \]

Positive = clearance, Negative = interference

Clearance Fits (a-h)

Always positive clearance - parts move/slide freely

H7/h6: Locational clearance
H7/g6: Sliding fit
H8/f7: Close running fit

Transition Fits (js-n)

May have clearance or interference depending on actual sizes

H7/js6: Snug fit, easy assembly
H7/k6: Push fit with light force
H7/n6: Tight, probable interference

Interference Fits (p-u)

Always interference - requires press or thermal assembly

H7/p6: Light press fit
H7/s6: Heavy press fit
H7/u6: Shrink fit

Surface Finish Recommendations

Fit Type	Hole Ra (μm)	Shaft Ra (μm)
Loose Running	3.2 - 6.3	1.6 - 3.2
Running/Sliding	1.6 - 3.2	0.8 - 1.6
Transition	0.8 - 1.6	0.4 - 0.8
Interference	0.8 - 1.6	0.4 - 0.8