How it works
An Ⓜ (maximum material condition) or Ⓛ (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
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 Ⓜ or Ⓛ 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 Ⓜ or Ⓛ 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.
Related calculators
- True Position Calculator — GD&T true position from X/Y deviation with MMC bonus tolerance and a pass/fail check.
- Composite Position Tolerance Calculator — Two-tier PLTZF/FRTZF position check from X/Y deviation.
- Flatness Tolerance Calculator — Flatness (surface form) from measured points, with a pass/fail check.
- Hole & Shaft Fit Calculator — ISO 286 hole-basis clearance-fit limits and clearance (H7/g6, H8/f7, …).
- Press Fit / Interference Calculator — Interference-fit contact pressure, assembly force, torque capacity and hub stress (Lamé).
- Cylindricity & Runout Calculator — Runout (TIR) and cylindricity zone from indicator and diameter readings.