ISO 286 IT grades — standard tolerances IT1 to IT18

The standard tolerance width for every ISO 286-1:2010 IT grade, in micrometres, across every size range from 1 to 500 mm.

Standard tolerance per grade and size (µm)

Scroll sideways for sizes above 30 mm →

Grade	≤ 3	3 – 6	6 – 10	10 – 18	18 – 30	30 – 50	50 – 80	80 – 120	120 – 180	180 – 250	250 – 315	315 – 400	400 – 500
IT1	0.8	1	1	1.2	1.5	1.5	2	2.5	3.5	4.5	6	7	8
IT2	1.2	1.5	1.5	2	2.5	2.5	3	4	5	7	8	9	10
IT3	2	2.5	2.5	3	4	4	5	6	8	10	12	13	15
IT4	3	4	4	5	6	7	8	10	12	14	16	18	20
IT5	4	5	6	8	9	11	13	15	18	20	23	25	27
IT6	6	8	9	11	13	16	19	22	25	29	32	36	40
IT7	10	12	15	18	21	25	30	35	40	46	52	57	63
IT8	14	18	22	27	33	39	46	54	63	72	81	89	97
IT9	25	30	36	43	52	62	74	87	100	115	130	140	155
IT10	40	48	58	70	84	100	120	140	160	185	210	230	250
IT11	60	75	90	110	130	160	190	220	250	290	320	360	400
IT12	100	120	150	180	210	250	300	350	400	460	520	570	630
IT13	140	180	220	270	330	390	460	540	630	720	810	890	970
IT14	250	300	360	430	520	620	740	870	1000	1150	1300	1400	1550
IT15	400	480	580	700	840	1000	1200	1400	1600	1850	2100	2300	2500
IT16	600	750	900	1100	1300	1600	1900	2200	2500	2900	3200	3600	4000
IT17	1000	1200	1500	1800	2100	2500	3000	3500	4000	4600	5200	5700	6300
IT18	1400	1800	2200	2700	3300	3900	4600	5400	6300	7200	8100	8900	9700

ISO 286-1 Table 1 prints sizes as rows; this table is the transpose, so each grade can be linked and highlighted as a single row.

Which grade for what

Grades	Typical use	Examples
IT1–IT4	Gauges and measuring instruments
IT5–IT6	Precision bearings, spindles	H6 g5 k5
IT7–IT8	General engineering fits	H7 g6 H8 f7
IT9–IT11	Rough fits, unmachined mating faces	H11 d9
IT12–IT18	Stamping, casting, general tolerances

How a grade becomes a limit

A tolerance class combines a fundamental deviation (a letter — see the fundamental deviation table) with an IT grade (a number, from this page) that sets the width of the zone. For example, IT7 = 21 µm at 18–30 mm; combined with hole letter H (zero line at EI) that gives H7 → 0 / +21 µm, and combined with shaft letter g it gives g6 → −20 / −7 µm. Pair a hole and a shaft class and the calculator works out the resulting fit.