ISO 2768 Tolerance Chart: How to Use It
ISO 2768-1:1989 supplies four general tolerance classes—f, m, c, and v—for covered linear and angular dimensions when a drawing explicitly invokes the standard. It does not apply automatically, and an individual tolerance beside a dimension takes precedence. This guide explains how to select the official table and range; obtain the controlling tolerance value from a licensed copy of the applicable edition.
Status checked 6 August 2026: ISO lists ISO 2768-1:1989, Edition 1, as published and current; it was last reviewed and confirmed in 2022. ISO 2768 Edition 2 is at stage 60.00, under publication, and is expected to replace it. Recheck the official catalogue before releasing a production drawing.
By MakerStage Engineering Team · Published
What ISO 2768-1 actually controls
A general tolerance fills a defined gap on a drawing. It does not replace engineering judgment or every feature-specific requirement.
A tolerance defines the acceptable variation around a nominal value. ISO 2768-1 simplifies drawings by letting one class cover specified kinds of dimensions that do not already have an individual tolerance. For broader machining capability and cost context, use the CNC tolerance selection guide.
The standard’s stated primary scope is parts produced by metal removal or formed from sheet metal. It notes that the tolerances may suit other materials, but that is not blanket permission to apply the same class to castings, molded plastics, weldments, or 3D printed parts without a suitable process standard and supplier agreement.
Covered when untoleranced
- Linear sizes, diameters, steps, radii, and distances
- External radii and chamfer heights on broken edges
- Angular dimensions, including right angles not governed by a referenced general geometrical-tolerance standard
- Dimensions created by machining assembled parts
Not governed by Part 1
- Dimensions with their own individual tolerances
- Dimensions covered by another referenced standard
- Bracketed auxiliary or reference dimensions
- Boxed theoretically exact dimensions
On a legacy drawing that invokes ISO 2768-2—such as through an mK designation—an unindicated right-angle relationship may fall under the applicable Part 2 perpendicularity rule rather than the Part 1 angular table. Confirm the feature and controlling drawing or contract before manufacturing or inspection.
Scope source: official ISO 2768-1 scope preview.
Swipe horizontally to read the complete decision diagram.
f, m, c, and v describe the selected tolerance class
The class letter chooses a column in the official standard. The resulting deviation still changes with size and characteristic type.
Fine
For ordinary linear dimensions, f is the tightest tabulated class where a value exists. For angular dimensions and broken edges, f and m use identical values.
Medium
A commonly encountered class, but not an automatic ISO default for CNC machining or every supplier.
Coarse
A wider general band for features whose function permits more variation. Critical fits still need explicit control.
Very coarse
For ordinary linear and angular dimensions, v is generally the widest tabulated class where a value exists. In the broken-edge table, c and v use identical values. Separately, some ordinary-linear class/range combinations have no tabulated value.
Use six checks before applying an ISO 2768-1 value
Use these six checks to choose the correct table, range, and class before calculating limits.
Read the controlling note
Confirm the drawing or specification invokes ISO 2768-1, identifies the edition or contractually accepted revision, and names class f, m, c, or v.
Check precedence and exclusions
Stop if an individual tolerance or another general-tolerance standard governs. Part 1 also excludes bracketed auxiliary or reference dimensions and boxed theoretically exact dimensions.
Classify the characteristic
Choose ordinary linear, external radius or chamfer height for a broken edge, or angular. Each category uses a different official table.
Select with the nominal metric value
Use the drawing nominal—not the measured result. For an angle, use the nominal length of the shorter side. Approximate inches never choose the row.
Consult the licensed table
Read the intersection of the controlling range and class in a licensed copy of the edition required by the controlling drawing or contract. Do not interpolate or invent a value where the table shows a dash.
Calculate and inspect
Calculate the bilateral limits, choose a capable measurement method, and apply the agreed conformity decision rule when uncertainty matters.
Swipe horizontally to compare the three lookup paths.
| Characteristic | Controlling nominal input | Official lookup path | Stop and clarify when |
|---|---|---|---|
| Ordinary linear dimension | Nominal size shown on the drawing | Linear-dimension table and invoked class | An individual tolerance, another standard, or no published value governs |
| External broken edge | Nominal external radius or chamfer height | Broken-edge table and invoked class | The feature is an internal fillet, another radius type, or outside the table scope |
| Angular dimension | Nominal length of the shorter side | Angular table and invoked class | The interval was selected from angle magnitude or measured length, or conflicts with a geometrical requirement |
Convert the selected deviation into limits
Let N be the nominal dimension and T the symmetric deviation retrieved from the licensed standard. Use the standard’s millimetre values to select ranges and calculate limits. If the drawing or inspection record uses inches, convert using 1 in = 25.4 mm exactly and round only to the documented resolution.
A breakpoint stays in its ending range
If the official row is written as “over A up to B,” a nominal value exactly equal to B remains in that row. Only a value above B moves forward.
Metric values control range selection
The standard uses millimetre values to select its ranges. Never select an interval from a rounded display conversion.
A dash is a stop sign, not zero
A dash means the selected class supplies no general value for that range. Specify the tolerance individually or obtain clarification.
Unsupported ranges need direct control
If the nominal value sits outside a published range or the selected cell supplies no value, specify the tolerance individually instead of extrapolating.
This workflow explains how to use the standard without replacing its normative tables. Obtain the controlling values from a licensed copy and confirm the live status on the official ISO 2768-1 record.
Ordinary linear dimensions use nominal-size ranges
Select the interval from the nominal metric dimension—not the measured result—then read the invoked class in a licensed copy of the standard.
Read the interval literally
If a row is written as “over A up to B,” it excludes A and includes B. A nominal value exactly equal to B remains in that row; only a value above B moves to the next interval. Do not interpolate between rows.
A dash is not zero tolerance
If the selected class supplies no value or the nominal sits outside the published range, the drawing needs an individual tolerance or engineering clarification. Never treat a missing value as zero or extrapolate one.
For production decisions, use the licensed edition required by the controlling drawing or contract, and verify its current catalogue status separately. This page explains the lookup method; it does not reproduce or replace the normative tables.
External radii and chamfer heights use a separate category
This category exists because a broken edge is specified differently from an ordinary size. Do not apply it to internal fillets or every radius on the part.
Confirm the feature
Use this category only for an external radius or chamfer height that breaks an edge. An internal fillet or a general radius is not automatically a broken-edge characteristic.
Select the interval
Use the nominal metric radius or chamfer height shown on the drawing—not a measured edge or rounded inch conversion—to select the interval in the licensed standard.
Angular ranges use the shorter side length
The nominal angle alone does not choose the deviation. Use the nominal length of the shorter side that forms the angle—not the measured result or nominal angle—to select the range.
Choose by side length
Use the nominal length of the shorter side shown on the drawing. Do not select the interval from the angle magnitude, the measured side, or a rounded unit conversion.
Read the invoked class
Once the licensed standard supplies angular deviation α, apply it bilaterally to the nominal angle. Do not substitute a geometrical-tolerance requirement.
Calculate angular limits symbolically
State the edition and class in the title block
A supplier cannot infer a class from the absence of individual tolerances. Make the governing note explicit and keep critical requirements beside their dimensions.
Clear title-block note
GENERAL DIMENSIONAL TOLERANCES: ISO 2768-1:1989, CLASS m.The shorter designation ISO 2768-m appears on many drawings. Including the part, edition, and class makes the intent easier to review during the current standard transition. The engineering drawing interpretation guide explains how title blocks, notes, dimensions, and revisions work together.
Drawing-release checklist
- 1Identify the units, drawing revision, ISO part and edition, and selected class.
- 2Place individual tolerances on fits, interfaces, stack-up drivers, and other function-critical dimensions.
- 3Specify current geometrical controls and datums where form, orientation, or location matters.
- 4State surface finish, thread class, burr or edge condition, and inspection needs separately; ISO 2768-1 does not supply them.
- 5Ask the supplier to confirm process capability before treating a class as manufacturable.
Make the requirement quote-ready
Add the title-block note, critical individual tolerances, and inspection requirements to the RFQ drawing requirements. MakerStage’s CNC milling and turning services include free DFM feedback with each RFQ.
Upload Your Drawing for a CNC QuotemK is a legacy combined callout
In ISO 2768-mK, m refers to Part 1 dimensional tolerances and K referred to a geometrical class in ISO 2768-2:1989. That second part is withdrawn.
Published
ISO 2768-1:1989
Current published dimensional edition as checked 6 August 2026.
Withdrawn
ISO 2768-2:1989
Withdrawn on 4 February 2021; legacy H, K, and L classes are not current guidance.
Replacement
ISO 22081:2021
ISO lists this as the new version following withdrawn Part 2. It defines rules for general geometrical and general size specifications, not a drop-in replacement for class K.
A withdrawn standard can still appear in a contract or legacy drawing. Do not erase or reinterpret that requirement without design authority. Confirm which revision governs, document the agreed disposition, and explicitly define current geometrical controls before manufacture.
Part 1 does not by itself control flatness, straightness, position, coaxiality, or runout. Use the geometric tolerancing fundamentals to separate size from form, orientation, and location.
Inspect the requirement that actually governs
Inspection is a decision sequence: identify the drawing requirement, choose the correct category and range, then use a suitable measurement method.
- 1Confirm drawing revision, units, title-block note, ISO edition, and class.
- 2Check for an individual tolerance or another governing standard before using the general class.
- 3Classify the characteristic as ordinary linear, external broken edge, or angular.
- 4Select the range from the nominal value, not the measured result.
- 5Treat a dash, missing value, or nominal outside the published range as a clarification request; do not extrapolate.
- 6Inspect geometrical requirements separately from size requirements.
- 7Account for measurement uncertainty near a specification limit and document the decision rule.
Who can accept an out-of-tolerance part?
ISO 2768-1 notes that exceeding a general tolerance does not necessarily impair function. That is not permission for a supplier or inspector to self-waive a nonconformance. Record the result and obtain a documented, design- or customer-authorized concession before accepting the part.
A characteristic near a limit needs an agreed conformity rule; a display value alone does not settle measurement uncertainty. The dimensional inspection methods guide compares practical inspection options and documentation.
Important limitations
This independently written educational guide uses symbolic calculations. It is not an ISO publication, is not endorsed by ISO, and does not reproduce the normative tolerance tables. It cannot replace the controlling drawing, a licensed copy of the applicable edition, or engineering review.
Frequently Asked Questions
What is ISO 2768?
What does ISO 2768-m mean on a drawing?
What does ISO 2768-mK mean?
What is the difference between ISO 2768 classes f, m, c, and v?
Is ISO 2768-2 still valid?
How do I find the ISO 2768 tolerance for a dimension?
Does ISO 2768 override a tolerance shown next to a dimension?
What is the difference between ISO 2768 and ISO 286?
Related Resources
Put the governing tolerances in the RFQ package
Include the drawing revision, ISO edition, selected class, individually toleranced critical features, and inspection requirements. MakerStage provides free DFM feedback with CNC machining RFQs.
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