ISO Fit Tolerance CalculatorISO FIT TOLERANCE

1. 1Enter the nominal size (e.g. a 25 mm shaft).
2. 2Pick a common fit from the quick list, or choose the hole and shaft deviation letters and IT grades separately.
3. 3Read the upper/lower deviations and the max/min sizes of hole and shaft — ready to put on the drawing.
4. 4Check the maximum/minimum clearance (or interference) and the fit type against your application.
5. 5Use the tolerance-zone diagram to see where both zones sit relative to the zero line.

ISO 286-1:2010 (JIS B 0401-1, CNS 4) names a tolerance class with a fundamental-deviation letter plus a grade, e.g. H7 or g6. The letter fixes the position of the zone relative to the zero line (the nominal size) — capitals A–ZC for holes, lower case a–zc for shafts — while the IT grade sets the width, IT5–IT18, smaller being finer. Tolerance values grow with size; all size ranges from 1 to 3150 mm are covered. Pairing a hole class with a shaft class gives a fit, classified by its maximum and minimum clearance as clearance, transition or interference.

H11/c11: loose running fit for coarse mechanisms; H9/d9: free running, low-precision bearings; H8/f7 and H9/f7: close running fit for lubricated plain bearings; H7/g6: sliding fit; H7/h6: locational clearance; H7/k6 and H7/js6: transition fits for locating gears and pulleys on shafts; H7/n6: tight location; H7/p6: light press fit; H7/s6 and H7/u6: press or shrink fits that can transmit torque on their own. Bearing housings commonly use H7, and shafts under bearing inner rings k5/m6.

All hole deviations A–ZC and shaft deviations a–zc (including CD, EF, FG), grades IT5–IT18 and nominal sizes 1–3150 mm are supported. Per the standard, a/b/c and A/B/C are defined only up to 500 mm, cd/ef/fg up to 10 mm, t from 24 mm, v from 14 mm and y from 18 mm; J and j exist only in grades 6–8 (hole) and 5–7 (shaft) and up to 500 mm. Undefined combinations are flagged.

孔 Hole: ES = EI + IT ; 軸 Shaft: ei = es − IT
a…h: es = −|fd| ; j…zc: ei = +fd ; A…H: EI = −es(a…h)
K, M, N (≤ IT8) / P…ZC (≤ IT7): ES = −ei + Δ, Δ = ITn − IT(n−1)
js / JS: ± IT / 2
Smax = ES − ei ; Smin = EI − es
Smin ≥ 0 → clearance ; Smax ≤ 0 → interference ; else transition

Results are for design reference only; confirm against supplier catalogues and the applicable standards before manufacturing.