GD&T · ASME Y14.5
True Position Calculator
Compute diametrical true position from measured X/Y deviations, apply MMC bonus tolerance automatically, and get an instant pass/fail against the position callout.
True position (diametrical)
TP = 2·√(Δx² + Δy²)Formulas used
True position: TP = 2 × √(ΔX² + ΔY²) — the diameter of the zone containing the actual axis
MMC bonus: allowed zone = stated tolerance + (actual mating size − MMC size) for an external feature; (MMC size − actual) for an internal feature.
Frequently asked questions
How is true position calculated?
Take the measured axis location minus the basic (nominal) location in X and Y, then TP = 2×√(ΔX²+ΔY²). The factor of 2 converts radial error to the diametrical zone used in the feature control frame.
What is MMC bonus tolerance?
When a feature departs from its maximum material condition (a hole drilled larger, a pin turned smaller), the position zone grows by the departure amount — giving credit for size while preserving assembly.