True Position Calculator
GD&T geometric dimensioning and tolerancing position analysis calculator
True Position Analysis
Feature Control Frame
Diameter of the cylindrical tolerance zone
Regardless of Feature Size - No bonus tolerance, position tolerance is constant
True Position (Basic Dimensions)
Basic dimension from secondary datum
Basic dimension from tertiary datum
Measured Dimensions (Actual Part)
Measured dimension from secondary datum
Measured dimension from tertiary datum
Position Offset Summary
⚠️ Quality Control Warning
• This calculator provides GD&T true position analysis for reference purposes
• Always verify measurements with calibrated precision instruments
• Consult ASME Y14.5 or ISO GPS standards for official GD&T requirements
• Consider measurement uncertainty and repeatability in acceptance decisions
• Parts exceeding position tolerance may cause assembly or functional issues
• Use qualified inspection personnel for critical dimensioning decisions
Example Calculation: Hole Position Analysis
Drawing Specifications
Feature: ⌀10.0 +0.05/-0.05 hole
Position Tolerance: ⌀0.05 Ⓜ |A|B|C|
True Position: 25.0mm from datum B, 15.0mm from datum C
Material Condition: MMC (Maximum Material Condition)
Measured Values
• Actual hole diameter: 10.02mm
• Measured position B: 25.02mm
• Measured position C: 14.98mm
• MMC size = 10.0 - 0.05 = 9.95mm
• Bonus tolerance = |10.02 - 9.95| = 0.07mm
• Position variation = 2 × √((25.0-25.02)² + (15.0-14.98)²) = 0.0566mm
• Total tolerance = 0.05 + 0.07 = 0.12mm
Result: PASS (0.0566 < 0.12)
Material Conditions
MMC Ⓜ
Maximum Material Condition - Hole smallest, shaft largest
LMC Ⓛ
Least Material Condition - Hole largest, shaft smallest
RFS
Regardless of Feature Size - No bonus tolerance
GD&T Symbols
Typical Position Tolerances
Understanding True Position and GD&T
What is True Position?
True position is a GD&T tolerance that controls the location of features relative to datums. It defines a cylindrical tolerance zone around the theoretically exact position where the feature's axis must lie. Unlike coordinate tolerancing, true position provides equal tolerance in all directions.
True Position Formula
PV = 2 × √((TB - MB)² + (TC - MC)²)
- PV: Position Variation from true position
- TB, TC: True position from datums B and C
- MB, MC: Measured position from datums B and C
- 2×: Converts radius to diameter (GD&T uses diametral zones)
Material Conditions
Maximum Material Condition (MMC)
When feature contains maximum material. Provides bonus tolerance when actual size deviates from MMC.
Least Material Condition (LMC)
When feature contains least material. Provides bonus tolerance when actual size deviates from LMC.
Regardless of Feature Size (RFS)
Position tolerance applies regardless of actual feature size. No bonus tolerance available.
Advantages of Position Tolerancing
- •57% more tolerance area than coordinate tolerancing
- •Equal tolerance in all directions
- •Bonus tolerance with material conditions
- •Direct relationship to functional requirements