True Position Calculator
Verify GD&T position tolerances instantly with our free online calculator. Improve assembly fit, reduce manufacturing costs, and ensure part compatibility with accurate position tolerance verification for engineering and manufacturing applications.
True Position Calculator
Calculation Results
How to Use This True Position Calculator
This calculator helps you verify if a feature’s location is within the specified position tolerance according to Geometric Dimensioning and Tolerancing (GD&T) standards.
- Select your preferred unit – Choose between millimeters or inches using the toggle button.
- Enter measured deviations – Input the X and Y deviations from the true position. For 3D calculations, include Z deviation.
- Specify the position tolerance – Enter the tolerance value from your engineering drawing.
- Select material condition – Choose RFS, MMC, or LMC based on your drawing requirements.
- View results instantly – The calculator automatically computes and displays the true position value and whether it passes or fails.
Example Calculation
With X deviation = 0.1mm, Y deviation = 0.15mm, and position tolerance = 0.5mm:
True Position = 2 × √(0.1² + 0.15²) = 2 × √(0.01 + 0.0225) = 2 × √0.0325 = 2 × 0.1803 = 0.3606mm
Since 0.3606mm ≤ 0.5mm, the feature passes the position tolerance check.
True Position Formulas Explained
Basic True Position Formula (2D)
True Position = 2 × √(ΔX² + ΔY²)
Where ΔX and ΔY are the deviations from true position in the X and Y directions respectively.
True Position Formula (3D)
True Position = 2 × √(ΔX² + ΔY² + ΔZ²)
For three-dimensional position control, the Z-axis deviation is included in the calculation.
With Bonus Tolerance (MMC/LMC)
Total Allowable Tolerance = Position Tolerance + Bonus Tolerance
When MMC or LMC modifiers are used, bonus tolerance is added to the base position tolerance based on the feature’s departure from its maximum or least material condition.
Common Applications of True Position
- Hole Patterns – Ensuring proper alignment of bolt holes in assemblies
- Mounting Features – Verifying position of mounting bosses, tabs, and slots
- Locating Pins – Checking position of dowel pins for accurate part alignment
- PCB Components – Verifying position of connectors and components on circuit boards
- Automotive Assembly – Ensuring proper fit of engine components, brackets, and fixtures
Diametric vs Rectangular Tolerance Zones
| Feature | Diametric Zone | Rectangular Zone |
|---|---|---|
| Tolerance Shape | Circular | Rectangular |
| Allowable Area | 57% more allowance | Standard |
| Common Usage | Most GD&T applications | Legacy or specific applications |
| Calculation | √(ΔX² + ΔY²) | |ΔX| + |ΔY| |
Frequently Asked Questions
True Position is a geometric tolerance that defines the permissible deviation of a feature (like a hole or pin) from its exact theoretical location. It’s specified using a positional tolerance zone within which the center point of the feature must lie.
These are material condition modifiers:
- MMC (Maximum Material Condition): The condition where a feature contains the maximum amount of material (largest shaft or smallest hole)
- LMC (Least Material Condition): The condition where a feature contains the least amount of material (smallest shaft or largest hole)
- RFS (Regardless of Feature Size): The tolerance applies regardless of the feature’s actual size
Bonus tolerance is the additional position tolerance available when a feature departs from its maximum material condition. For an external feature (shaft) at MMC, the bonus equals the difference between the MMC size and actual size. For an internal feature (hole), it’s the difference between actual size and MMC size.
Position controls the location of a feature relative to datums, while concentricity controls the coaxiality of features. Position is more commonly used and easier to measure than concentricity, which is why it’s preferred in most applications.
The current standard is ASME Y14.5-2018, published by the American Society of Mechanical Engineers. This standard defines the symbols, rules, and definitions for geometric dimensioning and tolerancing.