Engineering & PLMFree referencePDF, Excel, Word exportDiscrete Manufacturing

ISO 286 IT Tolerance Grades Table (IT5 to IT11, in microns)

ISO 286 defines standard tolerance grades, written IT01 to IT18, so that the width of a tolerance zone follows from just two things: the nominal size and the grade number. This table lists the grades most used in machining, IT5 to IT11, for sizes up to 500 mm.

Download:
Nominal size over - up to (mm)IT5 (um)IT6 (um)IT7 (um)IT8 (um)IT9 (um)IT10 (um)IT11 (um)
over 0 up to 3
4
6
10
14
25
40
60
over 3 up to 6
5
8
12
18
30
48
75
over 6 up to 10
6
9
15
22
36
58
90
over 10 up to 18
8
11
18
27
43
70
110
over 18 up to 30
9
13
21
33
52
84
130
over 30 up to 50
11
16
25
39
62
100
160
over 50 up to 80
13
19
30
46
74
120
190
over 80 up to 120
15
22
35
54
87
140
220
over 120 up to 180
18
25
40
63
100
160
250
over 180 up to 250
20
29
46
72
115
185
290
over 250 up to 315
23
32
52
81
130
210
320
over 315 up to 400
25
36
57
89
140
230
360
over 400 up to 500
27
40
63
97
155
250
400

Values are the total width of the tolerance zone in micrometres (1 um = 0.001 mm). Where a size sits exactly on a range boundary it belongs to the lower range. Confirm against your current copy of ISO 286-1 before releasing a drawing.

Check drawing tolerances against capability data

Optional: we can review how your ERP and PLM hold tolerance data and suggest where automated checks would help.

Optional. The tool and every export work without this. No spam.

How to use the table

Find the row that contains your nominal dimension, then read across to the grade you need. A 25 mm bore called out as H7 falls in the over 18 up to 30 row, so the zone width is 21 um. For an H hole the zone sits entirely above the basic size, giving 25.000 to 25.021 mm. For an h shaft the zone sits entirely below, giving 24.979 to 25.000 mm. The search box filters rows, so typing 30 jumps to the relevant size band.

What a grade number means

A lower IT number means a tighter tolerance and generally more machining cost. Typical processes: IT5 and IT6 are ground or honed work, IT7 and IT8 are precision turning, boring and reaming, IT9 to IT11 are normal turning, milling and drilling. Within one grade the width grows with size, because the standard bases the tolerance on a size factor that rises roughly with the cube root of the dimension. The grade fixes the width only. The position of the zone against the basic size is set separately by the fundamental deviation letter, such as H, g, k or p.

  • IT6 and IT7 are the usual pair for a hole and shaft running fit
  • IT11 is a reasonable default for non-critical machined features
  • Do not specify a tighter grade than the function needs

Worked example and reading the result

Take a 40 mm locating pin in a 40 mm hole, specified H7/g6. From the table the hole IT7 width is 25 um and the shaft IT6 width is 16 um. The hole runs 40.000 to 40.025. The g fundamental deviation then places the shaft slightly below basic size, so the fit is a clearance fit with a minimum clearance set by the g deviation and a maximum equal to that plus both zone widths. Use the companion hole and shaft worksheet to compute those limits.

Common mistakes

The most frequent error is confusing the grade width with the final limit deviations. The table gives width, not the upper and lower deviation. A second error is applying a grade chosen for a 10 mm feature to a 200 mm feature without checking the cost impact, since the same IT7 is 15 um at 8 mm but 46 um at 200 mm. A third is ignoring measurement uncertainty: if your gauge uncertainty is a third of the zone, you have no usable acceptance band at IT5 on small sizes.

Frequently Asked Questions

What does IT7 mean in ISO 286?

IT7 is international tolerance grade 7. It sets the width of the tolerance zone as a function of nominal size. For a 25 mm feature IT7 is 21 um. The grade does not say where the zone sits relative to basic size, which is controlled by the fundamental deviation letter.

Is a smaller IT number a tighter tolerance?

Yes. IT5 is much tighter than IT11 for the same nominal size. Each step of about five grades multiplies the zone width by roughly ten, so cost rises sharply as the number falls. Choose the loosest grade that still allows the part to function.

Why does tolerance width increase with size?

Larger parts are harder to make and measure to the same absolute accuracy, thermal effects grow, and the standard builds a size factor into every grade. The table shows this clearly, with IT7 going from 10 um at the smallest range to 63 um at the 400 to 500 mm range.

Does this table cover grades IT01 to IT4 and IT12 to IT18?

No. This reference stops at IT5 to IT11 because those are the grades used for most machined fits. Gauge making uses IT01 to IT4, and IT12 to IT18 cover rough and formed work. Refer to the full ISO 286-1 standard for those grades.

If drawing tolerances live in your PLM or ERP item master and you would like them checked against capability data automatically, we can build that. Netray works with partners on ERP-connected engineering data.

Talk to an ExpertExplore More Free Tools

Related Tools

Engineering & PLM

Hole and Shaft Fit Clearance Worksheet

An editable worksheet that computes minimum and maximum clearance (negative means interference) for each hole and shaft pair from their limit sizes.

Engineering & PLM

ISO 2768 General Tolerances Table

Look up the default tolerance for dimensions with no individual tolerance, by size range and ISO 2768-1 class.

Engineering & PLM

GD&T Symbols Reference Table

A searchable list of the 14 GD&T geometric characteristics and common modifiers with category, datum use and tolerance zone shape.

Engineering & PLM

Assembly Tolerance Stack Worst Case vs RSS Calculator

Add up the contributors in a linear stack and see the minimum gap by worst case, root-sum-square and a 1.5x modified RSS.

More Engineering & PLM tools

See all
Back to All Tools