What is inside
- ISO 286 IT grade table, 0-500 mm, grades IT6-IT12 in microns
- Which process actually holds which grade (turning vs grinding vs EDM)
- ISO 2768 f/m/c/v general tolerance table for unmarked dimensions
- How we read fit callouts like 25H7/g6 when quoting – and where drawings usually over-specify
Download it directly — no form, no email, no sales call. The chart is a one-page A4 PDF covering ISO 286 IT grades, the IT grade each process can actually hold, and ISO 2768 general tolerances for unmarked dimensions.
Download the tolerance chart (PDF)
Free to reuse and republish. If you do, a link back to https://meritmetalfab.com/tolerance-chart/ is appreciated.
1. ISO 286 IT grades (µm)
An IT grade is the width of the tolerance band for a given nominal size. Lower grade number means a tighter band. The practical translation: lathe and mill work lands at IT8–IT9, grinding reaches IT6–IT7, and every step tighter adds an operation and a cost line.
| Over – To (mm) | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 | IT12 |
|---|---|---|---|---|---|---|---|
| 0 – 3 | 6 | 10 | 14 | 25 | 40 | 60 | 100 |
| 3 – 6 | 8 | 12 | 18 | 30 | 48 | 75 | 120 |
| 6 – 10 | 9 | 15 | 22 | 36 | 58 | 90 | 150 |
| 10 – 18 | 11 | 18 | 27 | 43 | 70 | 110 | 180 |
| 18 – 30 | 13 | 21 | 33 | 52 | 84 | 130 | 210 |
| 30 – 50 | 16 | 25 | 39 | 62 | 100 | 160 | 250 |
| 50 – 80 | 19 | 30 | 46 | 74 | 120 | 190 | 300 |
| 80 – 120 | 22 | 35 | 54 | 87 | 140 | 220 | 350 |
| 120 – 180 | 25 | 40 | 63 | 100 | 160 | 250 | 400 |
| 180 – 250 | 29 | 46 | 72 | 115 | 185 | 290 | 460 |
| 250 – 315 | 32 | 52 | 81 | 130 | 210 | 320 | 520 |
| 315 – 400 | 36 | 57 | 89 | 140 | 230 | 360 | 570 |
| 400 – 500 | 40 | 63 | 97 | 155 | 250 | 400 | 630 |
2. Which process holds which IT grade
This is the table that decides most quoting arguments. If a drawing calls for IT6 on a milled pocket, the honest answer is that the pocket will be milled then ground or lapped — it is not a tighter program, it is a second operation.
| Process | Typical IT grade | Typical surface roughness Ra (µm) | Relative cost |
|---|---|---|---|
| Turning (CNC lathe) | IT8 – IT9 | 0.8 – 6.3 | Low |
| Milling (3-axis / 5-axis) | IT8 – IT9 | 0.8 – 6.3 | Low – mid |
| Reaming / boring | IT7 – IT8 | 0.8 – 3.2 | Mid |
| Grinding (cylindrical / surface) | IT6 – IT7 | 0.16 – 1.6 | High |
| Honing / lapping | IT5 – IT6 | 0.012 – 0.8 | High |
| Wire EDM | IT7 – IT8 | 1.6 – 6.3 | Mid – high |
| Drilling | IT10 – IT12 | 1.6 – 12.5 | Low |
3. ISO 2768 general tolerances (mm)
If a drawing only says “ISO 2768-m”, every dimension without its own tolerance gets the deviation below. F is fine, M is medium and the most common, C is coarse, V is very coarse. Medium is our default unless the drawing says otherwise.
| Nominal range (mm) | f (fine) | m (medium) | c (coarse) | v (very coarse) |
|---|---|---|---|---|
| 0.5 – 3 | ±0.05 | ±0.1 | ±0.2 | ±0.5 |
| 3 – 6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 |
| 6 – 30 | ±0.1 | ±0.2 | ±0.5 | ±1 |
| 30 – 120 | ±0.15 | ±0.3 | ±0.8 | ±1.5 |
| 120 – 400 | ±0.2 | ±0.5 | ±1.2 | ±2.5 |
| 400 – 1000 | ±0.3 | ±0.8 | ±2 | ±4 |
| 1000 – 2000 | ±0.5 | ±1.2 | ±3 | ±6 |
Linear dimensions are shown above. ISO 2768 also sets angular, straightness, flatness, perpendicularity, symmetry and run-out deviations under the same letter designations — the table above is the one that decides most quotes.
4. How we read tolerance callouts when quoting
- Holes and shafts. A fit like 25H7/g6 (ISO 286) means a hole of 25 mm with +21/0 µm and a shaft with −7/−20 µm. Every fit dimension is confirmed on the CMM before the batch ships.
- Tighter is not always better. Every IT grade below 8 usually adds an operation, normally grinding. If the part does not rotate or seal, IT9 may be all it needs.
- GD&T versus plus/minus. Position and profile callouts control how errors accumulate across features. Flat plus/minus tolerances on a chain of holes rarely reflect what the assembly actually needs.
- Material matters. Thin-wall aluminium and stainless move differently after machining. We stress-relieve and semi-finish, then finish to size, when the wall is thin enough for it to matter.
- Surface finish callouts. Ra 0.8 on a turned face is routine. Ra 0.4 and below usually means grinding or polishing — flag it early so it is priced rather than discovered.
Frequently asked questions
What does IT7 mean?
IT7 is a tolerance grade from ISO 286. For a nominal size between 18 and 30 mm it means a tolerance band of 21 µm — about 0.021 mm. In practice IT7 is a reamed or bored hole, or a ground diameter, rather than an as-milled feature.
What tolerance will I get if I do not specify one?
If the drawing states a general tolerance class such as ISO 2768-m, unmarked dimensions get the deviations in table 3 above. If the drawing states nothing at all, we quote to our standard general tolerance of ±0.05 mm on machined features and confirm the assumption in the quote.
Can you hold IT6 on a milled part?
Yes, but not by milling alone. IT6 on a milled feature means the feature is milled to leave stock and then ground or lapped to final size. That is a second operation with its own setup and inspection cost, which is why the quote changes when an IT6 callout appears.
How does surface finish relate to tolerance grade?
They travel together but are specified separately. A tighter tolerance generally forces a finer surface finish because the same process produces both, but a drawing can legitimately call for a tight tolerance with a rough finish, or a loose tolerance with a polished surface. Table 2 shows the typical pairing; treat the two callouts as independent requirements.
Should I use plus/minus tolerances or GD&T?
Use GD&T when the function depends on the relationship between features — hole position, flatness of a sealing face, perpendicularity of a bore. Use plus/minus for a single feature where only its own size matters. Applying flat plus/minus tolerances to a chain of holes usually either over-constrains the part or leaves the assembly to chance.
Is the ISO 2768 table the same for all materials?
The standard table is material-independent, but what a shop can actually achieve is not. Aluminium and brass hold tight general tolerances more easily than stainless or titanium, and thin walls distort in any material. The standard tells you what is permitted; the material tells you what is realistic.
Related pages
- How to Choose a Tolerance Grade — picking the loosest grade that still works.
- IT6 vs IT7 — what the step actually costs.
- H7 vs H8 — hole basis fit selection.
- Hole and Shaft Fit Selection Guide — reading fit callouts on a drawing.
- Ra vs Rz — the two roughness parameters, and which one your drawing means.
- How to Specify Surface Finish — turning a finish requirement into a callout.
- GD&T Basics for Buyers — datums, MMC and why the drawing is not a coordinate list.
- Thermal Expansion and Tight Tolerances — why a 200 mm part and a 20 mm part cannot share a rule.
- Metal Grade Cross Reference — AISI, EN, DIN, JIS and GB equivalents for 35 of those grades.
- Contact — send a drawing with a tolerance question.
Get a price for your part
Send a STEP file with the tolerance callouts, the material and the quantity. If a callout on the drawing is tighter than the part needs, we will say so and quote the looser option alongside it — most buyers save money on the first order that way.
Request a quote or email sales@techfoor.com.
Prefer the print version? Download the 2-page PDF — the same tables, laid out for A4.
Embed or cite this chart
You are welcome to quote or embed this tolerance chart on your own site, internal wiki or engineering document. The snippet below is self-contained and carries a link back to this page, so your readers can check which standard and size range a figure applies to.
<figure class="tf-cite">
<figcaption><strong>ISO 286 IT grades, ISO 2768 general tolerances and surface roughness by process</strong><br>
Source: <a href="https://meritmetalfab.com/tolerance-chart/">TechFoor CNC Tolerance Chart</a></figcaption>
<blockquote>IT grade table for 0-500 mm (IT6-IT12, in microns), ISO 2768 f/m/c/v general tolerances for unmarked dimensions, and the tolerance each machining process realistically holds.</blockquote>
</figure>Quoting a single number instead of the whole chart? Please still link back to https://meritmetalfab.com/tolerance-chart/. A print version of the same tables is available as a 2-page PDF.