How to use this calculator
- Choose the material condition. Select MMC or LMC and whether the feature is a hole (internal) or a pin (external).
- Enter the material-condition size. Enter the MMC or LMC limit: smallest hole / largest pin for MMC; largest hole / smallest pin for LMC.
- Enter the actual size. Enter the feature’s actual measured size.
- Enter the geometric tolerance. Enter the geometric tolerance stated at the modifier; read the bonus, the departure, and the total allowable tolerance.
How it works
An M (maximum material condition) or L (least material condition) modifier lets a geometric tolerance grow by the feature's departure from that material limit. The departure is the linear difference between the actual size and the limit: bonus = max(0, departure) and the total allowable tolerance is the stated geometric tolerance plus that bonus.
The direction of the departure depends on the feature. For an MMC hole the
bonus is actual − MMC; for an MMC pin it is MMC − actual.
LMC works the same way with the limits reversed: an LMC hole earns
LMC − actual and an LMC pin earns actual − LMC. A
feature at — or beyond — its material limit earns no bonus, so the bonus is
clamped to zero.
Worked example
Verified against the live calculator
A hole is called out at MMC 10.0 mm (the smallest allowed hole)
and actually measures 10.3 mm. Its departure from MMC is
10.3 − 10.0 = 0.3 mm, so it earns 0.3 mm of bonus. A
0.2 mm position tolerance at the modifier therefore becomes
0.2 + 0.3 = 0.5 mm of total allowable tolerance. The calculator
shows exactly this.
Frequently asked questions
What is bonus tolerance?
Bonus tolerance is extra geometric tolerance a feature earns when its size departs from the material-condition limit named by an MMC or LMC modifier. The bonus equals that departure and is added to the stated geometric tolerance.
How is MMC bonus tolerance calculated?
The bonus is the feature’s departure from its maximum-material size. For a hole MMC is the smallest size, so bonus = actual − MMC; for a pin MMC is the largest size, so bonus = MMC − actual. A bigger hole or smaller pin earns more.
What is the difference between MMC and LMC bonus?
They reference opposite limits. MMC is the most material (smallest hole / largest pin); LMC is the least material (largest hole / smallest pin). The departure is measured from whichever limit the modifier names, so the size that earns bonus is reversed: an LMC hole earns more as it gets smaller, an LMC pin as it gets larger.
Does RFS get any bonus tolerance?
No. Bonus tolerance only exists when the feature control frame carries an MMC or LMC modifier. Regardless of feature size (RFS) applies the full geometric tolerance at every size, with no bonus.
How does bonus add to position or orientation tolerance?
The bonus is added directly to the geometric tolerance at the modifier — position, perpendicularity, or any other applicable control. A 0.2 mm position tolerance with 0.3 mm of bonus gives 0.5 mm of total allowable tolerance for that feature.
Does this work in metric and imperial?
Yes — toggle SI/imperial anytime; the sizes, departure, bonus and total tolerance all convert.
Method & assumptions
- Bonus is the linear size departure from the material-condition limit named by the M or L modifier.
- Bonus can't be negative: a feature at or beyond its material limit gets none (and the actual size violates that limit).
- The bonus applies per-feature to the toleranced characteristic (position, orientation, etc.); for true position with a pass/fail check, use the true position calculator.