GO / NO-GO Gauge Tolerance Calculator

Plug and ring gauge sizes from the feature’s own tolerance — GO at the maximum material limit with its wear allowance, NO-GO at the least material limit — with the gauge maker’s tolerance, the Taylor principle that decides their shapes, and how much of the design band is left once the gauges have taken theirs.

Last updated 24 Sep 2026

GO / NO-GO gauge sizes

Feature class → both gauge sizes and what is left

Feature and its tolerance classA hole is checked by a plug gauge and a shaft by a ring or snap gauge, so the class also decides which gauge you are sizing. Pick “my own limits” to enter deviations directly.

Nominal size (mm)

My own upper deviation (µm)Used only with the last class option. Deviations from the nominal size, so a 25.000/25.033 hole is 0 and +33.

My own lower deviation (µm)

… and is that feature a bore or a shaft?Only read when you have chosen “my own limits”.

Gauge maker’s tolerance, as a % of the work toleranceThe ten per cent rule: industry practice divides 10% of the product tolerance between the GO and NO-GO gauges. It is a rule of practice rather than a requirement of any standard, and gauge standards instead publish fixed tolerance bands by size.

Wear allowance ruleTWO PUBLISHED RULES THAT DIFFER BY A FACTOR OF FIVE for the same gauge. Both are carried here and neither is averaged.

My own wear allowance, as a % of the work tolerance

Where the gauge tolerance goesA real standards fork. Inside means the gauge can only reject a borderline-good part and never accept a bad one; bilateral means half the gauge tolerance sits outside the work limit and a marginally bad part can pass.

Not a circuit: two bores in axial section with their gauges in them, and the tolerance band below. On the left the GO gauge is a FULL-FORM cylinder engaging the whole length of the bore at once, because it is standing in for the mating part and has to detect bowing and lobing as well as size. On the right the NO-GO is short and touches at two opposed points only, because it is looking for the one place the bore has gone past its largest limit. That difference in shape is Taylor's principle, and it is not a detail: a short GO plug passes a bent feature that measures correctly everywhere and will not assemble. Below, the full rectangle is the feature's own tolerance from its maximum material limit on the left to its least material limit on the right, and the two shaded strips are the GO gauge's zone (with its wear allowance) and the NO-GO's. Whatever they cover, the part does not get.

25.00165mmExample

A Ø25 H8 hole, gauged at the ten per cent rule with a wear allowance of 5% of the work tolerance, both gauge tolerances placed inside the work zone

Two gauges at the two limits, both made inwards

GO gauge = maximum material limit, shifted into the work zone by the wear allowance · NO-GO gauge = least material limit · gauge tolerance T_g = k · T_work (k ≈ 0.10) · band left for the part = T_work − 2·T_g − wear allowance

maximum material limit: the smallest hole or the largest shaft. The GO gauge is made to it, because that is the limit at which the feature still has to accept its mating part
least material limit: the largest hole or the smallest shaft. The NO-GO gauge is made to it, and must NOT enter or pass
T_g: the gauge maker’s tolerance. The ten per cent rule is industry practice, not a standard; gauge standards publish fixed bands by size instead
wear allowance: a deliberate offset on the GO gauge only, INTO the work zone, so the gauge has something to wear away before it reaches the work limit. Two published rules for it differ by a factor of five
band left: what the part actually gets. Both gauge tolerances and the wear allowance come out of the design tolerance, which is the point of this page

Worked example

A Ø25 H8 hole, gauged at the ten per cent rule with a wear allowance of 5% of the work tolerance, both gauge tolerances placed inside the work zone
The feature first. H8 at Ø25 is 0 to +33 µm, so the hole is 25.0000 to 25.0330 mm and the work tolerance is 33 µm. Its maximum material condition is the SMALLEST hole, 25.0000, and its least material condition the largest, 25.0330
The ten per cent rule gives each gauge a tolerance of 0.10 × 33 = 3.3 µm. That is a rule of industry practice rather than a requirement of any standard, and its published consequence is the point: it means up to ten per cent of good product may fail inspection, and that no bad product ever passes
The wear allowance, at 5% of the work tolerance, is 1.65 µm, and it applies to the GO gauge only. It is deliberately made INTO the work zone so the plug starts slightly oversize and has something to wear away before it reaches the work limit
So the GO plug's basic size is MMC plus the wear allowance = 25.0000 + 0.00165 = 25.00165 mm, with its 3.3 µm of gauge tolerance running upwards, into the work zone: 25.00165 to 25.00495. Its WEAR LIMIT is 25.0000 — when the plug has worn back to the hole's MMC it can no longer guarantee anything and must be scrapped
The NO-GO plug is made to the least material condition, 25.0330 mm, with its tolerance running DOWNWARDS, also into the work zone: 25.02970 to 25.03300. No wear allowance, because a NO-GO gauge that is doing its job barely enters anything and barely wears
Now add up what the part has left. Both gauge tolerances point inwards and the wear allowance does too: 2 × 3.3 + 1.65 = 8.25 µm of the 33 is gone, leaving 24.75 µm — 75% of the design band. The ten per cent rule costs a quarter of the tolerance, and it is worth knowing that before the drawing is signed
That is the cost of certainty. Place the gauge tolerances BILATERALLY about the work limits instead and the part keeps more of its band — but half of each gauge tolerance now lies OUTSIDE the work limit, so a hole up to 1.65 µm oversize can pass a NO-GO gauge that is in calibration. That is a real standards fork and not a rounding choice: the American practice puts the whole gauge tolerance inside, and the consequence is that no bad part ever passes
Finally, the shapes, which are the most useful thing here. The GO plug is a FULL-FORM cylinder engaging the whole hole at once, because it is standing in for the mating part and has to detect bowing and lobing as well as size. The NO-GO is short, or two opposed ball ends, because it is looking for the one place the hole has gone past its largest limit. Swap them and you get the commonest gauging failure there is: a short GO plug passes a bent or lobed feature that measures correctly everywhere and will not assemble

The Taylor principle, and why the two gauges are different shapes

This is the most useful thing on the page and it costs nothing to apply: the GO gauge is a copy of the mating part and checks whether the feature will assemble, while the NO-GO checks whether any part of it has gone past the other limit. A 19.98 mm shaft with a 0.03 mm bow needs a 20.01 mm ring to pass, so a full-form GO ring at 20.00 rejects it — and a two-point measurement reads 19.98 everywhere and finds nothing wrong. That is not a defect in either method; it is two different questions, and Taylor’s principle is the statement that a limit gauge has to ask both of them and ask each with the right shape.
	GO gauge	NO-GO gauge
What limit it checks	The MAXIMUM material condition — the smallest hole or the largest shaft	The LEAST material condition — the largest hole or the smallest shaft
Over what extent	The FULL engagement length of the feature, all at once	At a point, or on two opposed points
So what shape it is	A full-form cylinder for a hole, a full-form ring for a shaft. It is a copy of the mating part	A short plug, a pair of ball-ended or spherical contacts, or a blade anvil. Deliberately NOT full form
What it therefore controls	Size and FORM together. A bowed shaft of correct two-point size will not enter a full-form ring, and a lobed hole will not accept a full-form plug	Size only, and only locally. It is looking for the one place the feature has gone past its least material limit
What goes wrong if you swap them	A short GO plug passes a bent or lobed feature that will not assemble — the commonest gauging error there is, and it is invisible because the part measures correctly	A full-form NO-GO cannot enter an out-of-tolerance hole if the hole is bowed, so it passes a feature that is locally too large
The design consequence	The GO gauge physically enforces the envelope requirement, whatever the drawing says about it. That is why limit gauging sits naturally with ASME’s Rule #1 and needs the circled E under ISO	The NO-GO is why a feature can pass a gauge and still be rejected by a two-point measurement, or the reverse — they are different questions

Two published wear allowances for the same gauge, differing by a factor of five

Both of these are published, both are current, and they differ by five to one on the same gauge. The first rule takes the allowance from the WORK tolerance and the second from the GAUGE tolerance, which is itself only a tenth of the work tolerance — so 10% of the gauge tolerance is 1% of the work tolerance. Neither is averaged here and neither is presented as the answer. What decides it in practice is how the gauge is managed: a pre-shifted GO gauge with a generous allowance lasts longer before it has to be scrapped but rejects more good parts from new, while a gauge made close to the work limit with a WEAR LIMIT on its calibration certificate rejects nothing extra and is retired sooner. The third option in the list is the modern one, and it is also the one that needs a calibration system behind it. The same designation can mean different dimensions in different standards families — ANSI against ISO, inch against metric, one national standard against another. The family used here is named beside every figure; check which one your part was made to.
Rule	On a 25 H8 hole (µm)	As a % of the work tolerance	GO plug basic size (mm)	Work tolerance left (%)	Where it comes from
5% of the work tolerance	1.650	5.00	25.00165	75.0	Mech Codex’s limit-gauge design note and MetricMech’s go/no-go note both put the wear allowance at about 5% of the work tolerance, up to 10% where wear is severe.
10% of the gauge tolerance	0.330	1.00	25.00033	79.0	The classic metrology-textbook figure, which is 10% of the GAUGE tolerance and therefore only 1% of the work tolerance — five times smaller than the other rule for the same gauge.
none	0.000	0.00	25.00000	80.0	Gauge standards do not require a wear allowance at all; a wear LIMIT on the calibration certificate does the same job by retiring the gauge instead of pre-shifting it.

What the gauge standards actually publish, and what this page does instead

The honest position of this page is that it computes the ARITHMETIC of limit gauging — where each gauge sits, what it eats out of the design band, and what is left — and it does not reproduce any standard’s gauge tolerance table. Two reasons. The tables are copyrighted, and a gauge tolerance taken from a summarised web fetch is exactly the kind of number that arrives with a shifted column; four such fetches were caught in the making of this batch. Where you have a gauge standard to hand, use its band and put it in the percentage field. These dimensions come from a published standard’s table, not from a formula. The standard itself is cited below and the printed values are attributed to the catalogue they were taken from; a different publisher may round differently in the last digit.
Document	What it carries	How this page relates to it
ISO 1938-1:2015, plain limit gauges of linear size	The design and the tolerances for plain plug and ring gauges, as tables by size	Cited by number. Its tables are copyrighted and were not obtained, so this page computes the gauge sizes from the work tolerance and the published percentage rules instead of reproducing a gauge tolerance table. Where your gauge is bought to ISO 1938, the maker’s certificate is the authority and this page is the sanity check
ASME B89.1.5 and B89.1.6, master discs, plug gauges, master rings and ring gauges	The American gagemaker’s tolerance CLASSES, as fixed bands by size in inch units. The published charts that cite them carry XXX, XX, X, Y, Z and ZZ	Named, and the class bands are not printed: the charts that carry them hold the numbers in images this batch could not read, and a gauge tolerance transcribed wrongly is worse than none. Note for anyone comparing with other sources: there is no class “ZM” in these charts, whatever a secondary source may say
ASME B4.4M, inspection of workpieces	The American practice for placing a gauge’s tolerance relative to the work limits	The “inside” option on this page is that practice: both gauge tolerances lie within the work tolerance zone, so a gauge in calibration can reject a borderline-good part and can never accept a bad one
The ten per cent rule	Not in any standard. It is industry practice, published as such: “10% of the product tolerance is divided between the GO and NO GO gauges”	The default here, and adjustable. The consequence its own source states is worth printing: the rule means 10% of good product may fail inspection but no bad product ever passes
The four-to-one and ten-to-one measurement rules	The related and much older idea that the measurement’s uncertainty should be a quarter or a tenth of the tolerance	The same arithmetic seen from the metrology side. If the gauge tolerance is a tenth of the work tolerance, the gauge is a ten-to-one instrument — and at tight IT grades that becomes physically impossible, which is the warning this page gives when the gauge tolerance falls below a micrometre

Full form against two-point, and the quarter of your tolerance the gauges take

Two gauges, two limits, and both of them made inwards. The GO gauge is made to the feature’s maximum material limit — the smallest hole, the largest shaft — because that is the condition at which the feature still has to accept whatever mates with it. The NO-GO gauge is made to the least material limit and must not enter or pass. Both carry a gauge maker’s tolerance, commonly taken as ten per cent of the work tolerance, and the GO gauge carries a wear allowance as well. In the American practice all of that is placed INSIDE the work tolerance zone, so a gauge in calibration can reject a borderline-good part and can never accept a bad one.

Which means the gauges eat the design band, and by more than people expect. On a Ø25 H8 hole the work tolerance is 33 µm. The ten per cent rule takes 3.3 µm at each end and the wear allowance another 1.65, so 8.25 µm of the 33 is gone before the part is made and only 24.75 µm — 75 per cent — is actually available. A design tolerance is not what the part gets; it is what the part gets minus what the inspection takes. The good news is that the loss is entirely in the safe direction: every micrometre the gauges take is a good part rejected, never a bad part accepted. The bad news is that nobody tells the designer.

The Taylor principle, which is the most useful thing here. The GO gauge checks the maximum material condition over the FULL engagement length, all at once; the NO-GO checks the least material condition at a point. So a GO plug is a full-form cylinder and a GO ring is a full-form ring — a copy of the mating part — while a NO-GO is short, or a pair of ball-ended contacts, or a blade anvil, deliberately not full form. That is why they are different shapes, and the reason is functional: the GO gauge is asking whether the feature will assemble, which depends on form as well as size, and the NO-GO is asking whether any part of the feature has gone past the other limit, which is local. A 19.98 mm shaft with a 0.03 mm bow needs a 20.01 mm ring to pass, and a two-point measurement of it reads 19.98 everywhere and finds nothing wrong. Swap the shapes and you get the commonest gauging failure there is.

The wear allowance is a genuine standards fork and the difference is a factor of five. One published rule puts it at about five per cent of the WORK tolerance; another, the classic textbook figure, puts it at ten per cent of the GAUGE tolerance, which is one per cent of the work tolerance. Both are current and both are carried here; neither is averaged. What decides it is how the gauge is managed. A generously pre-shifted GO gauge lasts longer before it reaches its wear limit and rejects more good parts from new; a gauge made close to the work limit rejects nothing extra and has to be retired sooner, which is fine if and only if there is a calibration system that actually retires it. A third position — no allowance at all, and a wear LIMIT on the certificate — is the modern one and needs that system most.

Where this page stops. It computes the arithmetic of limit gauging and it does not reproduce any standard’s gauge tolerance table: ISO 1938-1’s tables are copyrighted and the ASME B89.1.5 class bands live in images this batch could not read, and a gauge tolerance transcribed with a shifted column is worse than none. If you have a class band to hand, put it in the percentage field. The feature’s own limits come from the ISO 286 fit calculator, the grade behind them from the IT grade tolerance calculator, and the temperature correction that matters once the gauge tolerance is down to a micrometre from the thermal effect on fit calculator.

Frequently asked questions

What size do I make a GO plug gauge?

To the hole’s maximum material condition — its SMALLEST allowed size — shifted into the work zone by the wear allowance, with the gauge tolerance running upwards from there. For a Ø25 H8 hole (25.0000 to 25.0330) at the ten per cent rule with a 5 per cent wear allowance, that is a basic size of 25.00165 mm with a tolerance of +0.0033/0, and a wear limit of 25.0000. The NO-GO plug goes at the largest allowed size, 25.0330, with its tolerance running downwards.

Is the 10% rule a standard?

No, and it is worth being clear about it. It is industry practice, published as such: ten per cent of the product tolerance divided between the GO and NO-GO gauges. The gauge standards do something different — ISO 1938 and the ASME B89.1 documents publish fixed tolerance bands by size, independent of the work tolerance, so a gauge for a tight feature and a loose one of the same diameter get the same band. The rule’s own source states its consequence plainly: up to ten per cent of good product may fail inspection, and no bad product ever passes.

Why is the NO-GO gauge a different shape from the GO gauge?

Taylor’s principle. The GO gauge checks the maximum material condition over the feature’s full engagement length, so it has to be a full-form copy of the mating part — a complete cylinder for a hole, a complete ring for a shaft — because it is asking whether the feature will assemble, and that depends on bowing and lobing as well as size. The NO-GO checks the least material condition at a point, so it is short or two-point, because it is asking whether any single place has gone past the other limit. A short GO plug is the commonest gauging error there is: it passes a bent feature that measures correctly and will not go together.

How much of my tolerance do the gauges take?

At the ten per cent rule with a five per cent wear allowance, twenty-five per cent — two lots of gauge tolerance and one wear allowance, all pointing inwards. On a Ø25 H8 hole that is 8.25 µm out of 33. The loss is entirely in the safe direction: it rejects good parts and never accepts bad ones. But it is real, it is invisible on the drawing, and if the designer expected the part to have the whole band then either the band or the gauge has to change.

Should the gauge tolerance go inside the work tolerance or straddle the limit?

Inside, if what you need is the guarantee that no out-of-tolerance part passes — and that is the American practice. Placing it bilaterally about the work limit keeps more of the band for the part, but half of each gauge tolerance then lies outside the limit, so a feature slightly beyond its limit can pass a gauge that is perfectly in calibration. This page computes both and reports exactly how much oversize a bilateral gauge could accept. If your specification says parts shall conform, bilateral placement does not deliver it.

What is a wear limit, and how is it different from a wear allowance?

A wear allowance is an offset built into the gauge when it is made, pushing the GO gauge into the work zone so it has something to wear away. A wear limit is a number on the calibration certificate: when the gauge has worn to it, it is scrapped. The limit is always the feature’s own maximum material limit, because past that the gauge is accepting parts the drawing does not allow. You can use either or both, and if you use no allowance at all — which is a defensible modern position — then the gauge is at its wear limit the day it is made and the calibration interval is doing all the work.

Related calculators

References

ISO 1938-1:2015, Geometrical product specifications (GPS) — Dimensional measuring equipment — Part 1: Plain limit gauges of linear size. Cited by number; the existence and title were confirmed on ISO’s catalogue during this batch, and a second edition is in preparation. Its tolerance tables are copyrighted and were not obtained, so this page computes the gauge sizes from the work tolerance and the percentage rules below instead of reproducing a gauge tolerance table, and says so.
ASME B89.1.5-1998, Measurement of Plain External Diameters for Use as Master Discs or Cylindrical Plug Gages, and ASME B89.1.6-2002, Measurement of Plain Internal Diameters for Use as Master Rings or Ring Gages — the documents that carry the American gagemaker’s tolerance classes. The classes published in the charts that cite them are XXX, XX, X, Y, Z and ZZ, in inch units, each a fixed band by size rather than a percentage of the work tolerance. NOTE for anyone comparing this page with the brief that asked for it: there is no class “ZM” in these charts. Vermont Gage’s and Judge Tool’s published ASME B89.1.5 charts both run XXX to ZZ, and the chart values themselves are held in images this batch could not read, so no class band is printed here.
Thread Check Inc. How to determine the proper gagemaker tolerance for a GO/NO GO cylindrical gaging application. The source for the ten per cent rule as industry practice: “This common rule of practice requires that 10% of the product tolerance is divided between the GO and NO GO gauges”, and for its consequence, that the rule “results in the possibility that 10% of good product may fail inspection but that no bad product would ever pass inspection”. Also the source for the direction: a plus tolerance on a GO plug and a minus tolerance on the NO GO, reversed for a ring gauge.
Mech Codex. Limit gauge design: GO/NO-GO gauging, Taylor’s principle and gauge tolerancing. The source for Taylor’s principle as stated on this page — the GO gauge a full-form replica of the feature at its maximum-material limit engaging over its full length, the NO-GO checking the least-material limit point by point with minimal contact — and for the 5 per cent wear allowance on the GO member only. Its two worked gauges, a Ø25 H8 plug and a Ø40 g6 snap, are reproduced here exactly.
MetricMech. Go/no-go gauges: sizing, 10% rule and wear limits, citing IS 3455 / ISO 1938. The second source for the same two rules, and the source for the statement that both gauge tolerances point INTO the work tolerance band so that “the gauge can only reject a borderline-good part, never accept a bad one”.
The classic metrology-textbook wear allowance, reported in several teaching sources as 10 per cent of the GAUGE tolerance rather than of the work tolerance. That is 1 per cent of the work tolerance, five times smaller than the other published rule for the same gauge, and this page prints both rather than averaging them. Recorded as a secondary source: the primary standards were not obtained.
ISO 286-1:2010, Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes — Part 1: Basis of tolerances, deviations and fits. Cited by number; the standard is copyrighted and its tables are not reproduced here. What this page uses from it is its STRUCTURE, which is not a table: the standard tolerance factor i = 0.45·∛D + 0.001·D evaluated at the geometric mean of each nominal size step, the grade multipliers (IT5 = 7i, IT6 = 10i, IT7 = 16i, IT8 = 25i, IT9 = 40i, IT10 = 64i, IT11 = 100i and so on), the rule that IT(n+5) is ten times IT(n) from IT7 upward, the formulas for each letter’s fundamental deviation, and the Δ correction for hole letters J to ZC. Every one of those is checked here against a published table rather than trusted.