True Position Calculator
Calculate GD&T true position tolerance per ASME Y14.5: TP = 2√(Δx² + Δy²).
Formula
TP = 2√(Δx² + Δy²) [2D]; TP = 2√(Δx² + Δy² + Δz²) [3D] (ASME Y14.5)
- Δx = actual X − nominal X; similarly for Δy and Δz.
- Result is the diameter of the cylindrical tolerance zone.
- If TP ≤ stated tolerance on drawing, the feature is in tolerance.
2D: nominal (50, 30), actual (50.3, 30.4)
Inputs
- Dimensions: 2d
- Nominal X: 50 mm
- Actual X: 50.3 mm
- Nominal Y: 30 mm
- Actual Y: 30.4 mm
- Nominal Z: 0 mm
- Actual Z: 0 mm
Δx=0.3, Δy=0.4. TP = 2√(0.09 + 0.16) = 2√0.25 = 2 × 0.5 = 1.000 mm
Frequently asked questions
Why multiply by 2?
The position deviation is the radius of the actual tolerance zone; multiplying by 2 converts to diameter, matching the drawing callout format ⌀TP.