ISO 286 Fits & Tolerances Calculator

ISO 286 Standard Tolerance Factor and IT Grade

i = 0.45 · D^(1/3) + 0.001 · D | IT = round( i · f ) | with | f: IT1 = 0.8, IT2 = 1.2, IT3 = 2, IT4 = 3, IT5 = 7, IT6 = 10, IT7 = 16, IT8 = 25, IT9 = 40, IT10 = 64, IT11 = 100, IT12 = 160, IT13 = 250, IT14 = 400, IT15 = 640, IT16 = 1000. | Note on the argument: ISO 286-1 evaluates i at D_m, the geometric mean of the nominal size step, and tabulates grades below IT5 rather than deriving them from i. This tool evaluates i at the entered D, so grades IT8 and coarser sit ~2-4 % above the ISO 286-2 table (at ø25: IT9 = 54 μm here vs 52 μm tabulated, IT7 = 21 μm agrees).

Variables: i = standard tolerance factor (μm), D = nominal diameter as entered into this tool (mm), D_m = geometric mean of the ISO nominal size-step limits, the argument ISO 286-1 itself uses in place of D (mm), IT = width of the tolerance zone for the selected grade (μm), f = grade multiplier (dimensionless). Applicable nominal size range 1-500 mm. Source: ISO 286-1:2010, ISO code system for tolerances on linear sizes - standard tolerance factor i and IT grades; numerical comparison against ISO 286-2:2010 tables of standard tolerance values

Fundamental and Limit Deviations (H hole with a-h shaft)

Hole H: EI = 0 , ES = EI + IT_hole | Shaft a-h: the fundamental deviation is the upper deviation es (≤ 0), and ei = es − IT_shaft , with | es_a = −(265 + 1.3 · D_m) , es_b = −(140 + 0.85 · D_m) , es_c = −52 · D_m^0.2 , es_d = −16 · D_m^0.44 , es_e = −11 · D_m^0.41 , es_f = −5.5 · D_m^0.41 , es_g = −2.5 · D_m^0.34 , es_h = 0 | D_m = √(D₁ · D₂) | Scope: these are the classes this tool reproduces against ISO 286-2 (e.g. H7/h6, H7/g6, H7/f6, H8/e8). Transition and interference shafts (js, k, m, n, p, r, s, t, u, x) and every hole letter other than H are returned with inverted sign by this tool and must be checked against the ISO 286-2 tables.

Variables: EI = lower deviation of the hole (μm), ES = upper deviation of the hole (μm), es = upper deviation of the shaft, equal to its fundamental deviation for letters a-h (μm), ei = lower deviation of the shaft (μm), IT_hole and IT_shaft = tolerance-zone widths for the selected grades from the equation above (μm), D_m = geometric mean of the bounds of the ISO nominal size step containing D (mm; for ø25 the step is 18-30 mm so D_m = √(18·30) = 23.24 mm), D₁ and D₂ = lower and upper bound of that size step (mm). Source: ISO 286-1:2010 (fundamental deviation formulae for shafts a-h and holes A-H); limit deviations cross-checked against ISO 286-2:2010 tables

Limit Sizes of Hole and Shaft

D_max = D + ES/1000 | D_min = D + EI/1000 | d_max = D + es/1000 | d_min = D + ei/1000

Variables: D = nominal (basic) size common to hole and shaft (mm), D_max and D_min = maximum and minimum hole diameter (mm), d_max and d_min = maximum and minimum shaft diameter (mm), ES and EI = upper and lower deviation of the hole (μm), es and ei = upper and lower deviation of the shaft (μm). The factor 1000 converts deviations in μm to mm. Source: ISO 286-1:2010, basic size, deviations and limits of size

Clearance, Interference and Fit Classification

C_max = D_max − d_min | C_min = D_min − d_max | Clearance fit if C_min ≥ 0 | Transition fit if C_min < 0 ≤ C_max | Interference fit if C_max < 0 , the interference being −C

Variables: C_max = maximum clearance (mm), C_min = minimum clearance (mm), a negative value of either being an interference of magnitude −C, D_max and D_min = hole limits (mm), d_max and d_min = shaft limits (mm). The tool reports both quantities as absolute values in μm (1 mm = 1000 μm) and relabels them Max/Min interference when the corresponding value is negative. Worked example at ø25 H7/f6: D 25.000/25.021 mm, d 24.967/24.980 mm, C_min = 20 μm, C_max = 54 μm, clearance fit. Source: ISO 286-1:2010, clearance, interference and the three types of fit