ISO 286 standard tolerance grades IT01 to IT18

The standard tolerance grade (IT) sets the width of a tolerance zone; the number in a class such as H7 or g6 is its grade. The width grows with the grade and with the nominal size.

Grades IT01 to IT11 in micrometres, IT12 to IT18 in millimetres, as the standard prints them. “—”: no value in the standard for that size. ISO fits explained

Nominal size (mm)		IT01	IT0	IT1	IT2	IT3	IT4	IT5	IT6	IT7	IT8	IT9	IT10	IT11	IT12	IT13	IT14	IT15	IT16	IT17	IT18
over	up to	µm	µm	µm	µm	µm	µm	µm	µm	µm	µm	µm	µm	µm	mm	mm	mm	mm	mm	mm	mm
0	3	0.3	0.5	0.8	1.2	2	3	4	6	10	14	25	40	60	0.1	0.14	0.25	0.4	0.6	1	1.4
3	6	0.4	0.6	1	1.5	2.5	4	5	8	12	18	30	48	75	0.12	0.18	0.3	0.48	0.75	1.2	1.8
6	10	0.4	0.6	1	1.5	2.5	4	6	9	15	22	36	58	90	0.15	0.22	0.36	0.58	0.9	1.5	2.2
10	18	0.5	0.8	1.2	2	3	5	8	11	18	27	43	70	110	0.18	0.27	0.43	0.7	1.1	1.8	2.7
18	30	0.6	1	1.5	2.5	4	6	9	13	21	33	52	84	130	0.21	0.33	0.52	0.84	1.3	2.1	3.3
30	50	0.6	1	1.5	2.5	4	7	11	16	25	39	62	100	160	0.25	0.39	0.62	1	1.6	2.5	3.9
50	80	0.8	1.2	2	3	5	8	13	19	30	46	74	120	190	0.3	0.46	0.74	1.2	1.9	3	4.6
80	120	1	1.5	2.5	4	6	10	15	22	35	54	87	140	220	0.35	0.54	0.87	1.4	2.2	3.5	5.4
120	180	1.2	2	3.5	5	8	12	18	25	40	63	100	160	250	0.4	0.63	1	1.6	2.5	4	6.3
180	250	2	3	4.5	7	10	14	20	29	46	72	115	185	290	0.46	0.72	1.15	1.85	2.9	4.6	7.2
250	315	2.5	4	6	8	12	16	23	32	52	81	130	210	320	0.52	0.81	1.3	2.1	3.2	5.2	8.1
315	400	3	5	7	9	13	18	25	36	57	89	140	230	360	0.57	0.89	1.4	2.3	3.6	5.7	8.9
400	500	4	6	8	10	15	20	27	40	63	97	155	250	400	0.63	0.97	1.55	2.5	4	6.3	9.7
500	630	—	—	9	11	16	22	32	44	70	110	175	280	440	0.7	1.1	1.75	2.8	4.4	7	11
630	800	—	—	10	13	18	25	36	50	80	125	200	320	500	0.8	1.25	2	3.2	5	8	12.5
800	1000	—	—	11	15	21	28	40	56	90	140	230	360	560	0.9	1.4	2.3	3.6	5.6	9	14
1000	1250	—	—	13	18	24	33	47	66	105	165	260	420	660	1.05	1.65	2.6	4.2	6.6	10.5	16.5
1250	1600	—	—	15	21	29	39	55	78	125	195	310	500	780	1.25	1.95	3.1	5	7.8	12.5	19.5
1600	2000	—	—	18	25	35	46	65	92	150	230	370	600	920	1.5	2.3	3.7	6	9.2	15	23
2000	2500	—	—	22	30	41	55	78	110	175	280	440	700	1100	1.75	2.8	4.4	7	11	17.5	28
2500	3150	—	—	26	36	50	68	96	135	210	330	540	860	1350	2.1	3.3	5.4	8.6	13.5	21	33

Source and verification

Standard

ISO 286-1:2010 Geometrical product specifications (GPS) - ISO code system for tolerances on linear sizes - Part 1: Basis of tolerances, deviations and fits; ISO 286-2:2010 Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts

Verification

primary (the standard’s own text was seen)

Verified from

https://cdn.standards.iteh.ai/samples/54915/7d6147c29fed4e31af36b60561e88752/ISO-286-2-2010.pdf (ISO 286-2:2010 preview: Table 1; Tables 2 and 3 for holes A to E)
https://law.resource.org/pub/in/bis/S01/is.919.1.1993.pdf (IS 919 (Part 1):1993, identical with ISO 286-1:1988: clause 9, Tables 2 and 3, Annex A)
https://cdn.standards.iteh.ai/samples/45975/c0a5df14167f48eebc6c17dc4da5f9c4/ISO-286-1-2010.pdf (ISO 286-1:2010 preview: terms and definitions only, no tables)

Verification notes

itGrades: ISO 286-2:2010 Table 1 (reproduced there from ISO 286-1:2010), read from the standard's own preview on 2026-10-22. IT01 and IT0 are not given above 500 mm (null).
fundamentalDeviations: read from ISO 286-1:1988 Tables 2 (shafts) and 3 (holes) in the identical Indian adoption IS 919 (Part 1):1993. The 2010 edition's Tables 2 and 3 were not seen. Holes A, B, C, D and E were cross-checked against ISO 286-2:2010 Tables 2 and 3 (lower limit deviations EI) and agree for every size step up to 500 mm. The other letters come from the 1988 edition only (see docs/to-verify.md).
The Delta values equal IT(n) - IT(n-1) of itGrades for every step above 3 mm; scripts/check-library.mjs checks this.

This table

ISO 286-2:2010, Table 1 "Values of standard tolerance grades for nominal sizes up to 3 150 mm" (from ISO 286-1:2010, Table 1). Converted to mm; one value per entry of sizeSteps (main-step values repeated over their intermediate steps).

Data file

library/fits/iso-286.json

Values that could not be checked against the standard are left out and listed in docs/to-verify.md. Check the standard itself before you rely on a value for production, and report any mistake on GitHub. to-verify.md · Issues