GD&T Positional Tolerance Calculator
Calculate bonus tolerance, total positional tolerance, and virtual condition size for a GD&T true-position callout at MMC or RFS, then check a measured X/Y deviation from true position against the result — pass, fail, and margin.
Input
A hole's MMC is its smallest permitted diameter (most material); a shaft's MMC is its largest permitted diameter.
MMC lets the feature earn bonus tolerance as its produced size departs from MMC toward LMC. RFS — the default when the feature control frame shows no modifier — applies the specified tolerance at every produced size, with no bonus.
The diametral tolerance zone specified in the feature control frame, e.g. the 0.30 in ⌖⌀0.30Ⓜ|A|B|C.
The size limit at MMC — a hole's lower size limit, or a shaft's upper size limit.
The feature's produced size from inspection — used to work out how much bonus tolerance it has earned.
Leave blank to skip the pass/fail check. Can be positive or negative.
Leave blank to skip the pass/fail check. Can be positive or negative.
Output
Position Tolerance Result
| Metric | Value |
|---|---|
| No data yet | |
Measured Position Check
| Metric | Value |
|---|---|
| No data yet | |
Guides
Work out how much positional tolerance a toleranced feature actually has — including any bonus earned from its material condition modifier — and check a measured X/Y deviation against it.
How to use it
- Pick the feature type — Hole for an internal feature, Shaft / pin for an external one. This decides which direction bonus tolerance and virtual condition move.
- Pick the material condition modifier shown in the feature control frame:
- MMC (Ⓜ) — the feature earns bonus tolerance as its produced size departs from MMC toward LMC. Enter the feature size at MMC (a hole's lower size limit, a shaft's upper size limit) and the actual measured size.
- RFS — the default when the feature control frame shows no modifier at all. The specified tolerance applies at every produced size; there's no bonus.
- Enter the positional tolerance from the feature control frame (the diametral value, e.g. the 0.30 in ⌖⌀0.30Ⓜ|A|B|C).
- Read the Position Tolerance Result for the bonus tolerance, total positional tolerance, and (at MMC) the virtual condition size for gauge sizing.
- Optionally enter a measured X/Y deviation from true position — from a CMM report or manual layout check — to get the diametral positional deviation and a pass/fail against the total tolerance, with margin.
Bonus tolerance
Bonus tolerance is the extra positional tolerance a feature earns beyond what's printed in the feature control frame, because its produced size isn't at the worst case (MMC):
- Hole (internal feature): MMC is the smallest permitted diameter (most material). As the produced hole gets larger, it earns bonus =
actual size − MMC size. - Shaft / pin (external feature): MMC is the largest permitted diameter (most material). As the produced shaft gets smaller, it earns bonus =
MMC size − actual size. - RFS: always zero, regardless of produced size.
Total positional tolerance = specified tolerance + bonus.
Virtual condition
Virtual condition is the worst-case boundary combining size and position at MMC — the number a functional gauge is built to:
- Hole:
VC = MMC size − positional tolerance - Shaft:
VC = MMC size + positional tolerance
It isn't a single fixed value under RFS (the boundary moves with whatever size is actually produced), so this tool only reports it for MMC.
Measured position check
Enter the X and Y deviation of the produced feature's actual center from its true (nominal) position — the numbers a CMM or layout inspection report gives you. The diametral positional deviation is 2 × √(dx² + dy²); it passes when that's within the total positional tolerance above.
Limits
This is a checking aid for drawing review and estimation — not a substitute for full ASME/ISO GD&T interpretation, datum simulation, inspection strategy, or gauge design. It doesn't account for datum feature shift, multiple datum references, or composite/multi-segment feature control frames. Verify against the actual drawing and your inspection method before using for production acceptance decisions.
Privacy
Everything runs in your browser — no dimensions or measurements leave your machine.
Related tools
For a chain of dimensions rather than a single positional callout, see the Tolerance Stackup Calculator. For sizing an interference fit, see the Press Fit Interference Calculator. For standard ISO fit/tolerance classes, see the Fits Tolerances ISO Helper.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/gdt-positional-tolerance-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"featureType": "hole",
"materialCondition": "mmc",
"positionTolerance": "0.30",
"conditionSize": "9.80",
"actualSize": "9.95",
"measuredDx": "0.10",
"measuredDy": "0.05"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `gdt-positional-tolerance-calculator` tool (GD&T Positional Tolerance Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.