Bonus Tolerance (MMC) Position Calculator
When a position tolerance carries the MMC modifier, the feature is allowed extra position tolerance as it moves away from maximum material condition. This calculator applies that rule and tells you whether the measured position is inside the resulting zone.
Your numbers
Smallest size for a hole, largest size for a pin.
Largest size for a hole, smallest size for a pin.
Your results
Assumes the hole or pin is within its size limits and the callout uses MMC or LMC as the position modifier. If the feature is RFS no bonus applies. Verify against your drawing standard (ASME Y14.5 or ISO 2692).
Total allowed position tolerance vs actual size
Sweeps Measured actual size from 8 to 8.1, holding your other inputs fixed.
Automate position checks from CMM output
Optional review of how measured data could be evaluated and recorded in your ERP.
Optional. The tool and every export work without this. No spam.
How to use it
Pick whether the feature is a hole or a pin and whether the position callout uses MMC or LMC. Enter the size limits, the measured actual size, the stated position tolerance and the measured offsets from true position along X and Y. The calculator returns the bonus tolerance, the total allowed diameter, the measured diametral error and the margin.
The formula
For a hole at MMC, the bonus equals actual size minus MMC size, where MMC is the smallest hole. For a pin at MMC, the bonus is MMC size minus actual size, where MMC is the largest pin. The total tolerance is the stated tolerance plus the bonus. Measured position error is two times the radial distance from true position, because tolerance is stated as a diameter.
- Hole at MMC: bonus = actual - MMC size
- Pin at MMC: bonus = MMC size - actual
- Total = stated tolerance + bonus
- Position error (diameter) = 2 x sqrt(x^2 + y^2)
Worked example and mistakes
A hole of 8.00 to 8.10 mm with 0.20 position at MMC, measured at 8.06 mm, gains 0.06 bonus for a total 0.26 mm zone. Offsets of 0.08 and -0.10 give a diametral error of about 0.256 mm, so it passes with a small margin. Typical mistakes are forgetting to double the radial offset and applying bonus to RFS callouts.
Frequently Asked Questions
What is bonus tolerance?
It is additional geometric tolerance permitted when a feature of size departs from its maximum (or least) material condition. The looser the fit of the actual size, the more position error the assembly can absorb.
Does bonus apply to the datum features?
A separate rule applies. Datum feature of size with a material condition modifier can allow datum shift, which is not covered here. This calculator handles only the toleranced feature.
Why is the error doubled?
A position tolerance is a cylindrical zone with a stated diameter. The radial distance from true position must fit within half of that diameter, so the diametral error is twice the radial offset.
What if the size is outside the limits?
Then the part fails the size requirement regardless of position. Check the size first, because bonus is only valid within the size tolerance.
If position results are keyed into your ERP by hand, we can look at calculating and recording the pass or fail directly from CMM output.
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