📐 True Position Calculator
Calculate true position tolerance
Diameter tolerance (⌀)
How to Use This Calculator
Select Tolerance Type
Choose diameter tolerance (⌀) or radius tolerance (R). Diameter tolerance is most common for true position (⌀ 0.005).
Enter Nominal Position
Input nominal (theoretical) X and Y positions in inches. These are the ideal positions from the design drawing.
Enter Actual Position
Input actual (measured) X and Y positions in inches from inspection or CMM measurements.
Enter Tolerance and Calculate
Input tolerance in inches (⌀ for diameter, R for radius). Click "Calculate True Position" to see position deviation, tolerance zone, and compliance status.
Formula
Position Deviation = √((Actual X - Nominal X)² + (Actual Y - Nominal Y)²)
Tolerance Zone (radius) = Tolerance / 2 (for diameter tolerance)
Within Tolerance: Position Deviation ≤ Tolerance Zone
Example 1: Nominal (0, 0), Actual (0.001, 0.002), Tolerance ⌀ 0.005
Step 1: Deviation X = 0.001 - 0 = 0.001"
Step 2: Deviation Y = 0.002 - 0 = 0.002"
Step 3: Position Deviation = √(0.001² + 0.002²) = √(0.000005) = 0.0022"
Step 4: Tolerance Zone = 0.005 / 2 = 0.0025" (radius)
Step 5: 0.0022 ≤ 0.0025 → Within Tolerance ✓
Example 2: Nominal (1.0, 1.0), Actual (1.003, 1.002), Tolerance ⌀ 0.010
Step 1: Position Deviation = √((1.003-1.0)² + (1.002-1.0)²) = √(0.000009 + 0.000004) = 0.0036"
Step 2: Tolerance Zone = 0.010 / 2 = 0.005" (radius)
Step 3: 0.0036 ≤ 0.005 → Within Tolerance ✓
About True Position Calculator
The True Position Calculator is an essential tool for quality engineers, machinists, and inspection personnel who need to calculate true position tolerance and deviation for GD&T (Geometric Dimensioning and Tolerancing) applications. This calculator implements standard true position formulas based on nominal and actual positions, helping you verify dimensional compliance and ensure part quality.
When to Use This Calculator
- Quality Inspection: Calculate true position deviation for part inspection
- GD&T Analysis: Verify true position tolerance compliance
- CMM Measurements: Analyze CMM measurement results for true position
- Part Validation: Validate part dimensions against drawing specifications
- Educational Use: Learn and understand true position calculations
Why Use Our Calculator?
- ✅ Accurate Formulas: Uses standard true position equations
- ✅ Dual Tolerance Types: Supports diameter (⌀) and radius (R) tolerances
- ✅ Complete Analysis: Shows position deviation, tolerance zone, and compliance status
- ✅ Easy to Use: Simple inputs for nominal and actual positions
- ✅ Time Savings: Instant calculations eliminate manual math
Understanding True Position
Basic Principle: True position is a GD&T symbol (⌀) that specifies the exact location of a feature. Position deviation is calculated as the distance from actual position to nominal position: Deviation = √((Actual X - Nominal X)² + (Actual Y - Nominal Y)²). The feature must be within the tolerance zone (circular zone centered at nominal position).
Tolerance Zone: Tolerance zone is a circular zone centered at nominal position. For diameter tolerance (⌀), zone radius = tolerance / 2. For radius tolerance (R), zone radius = tolerance. Position deviation must be ≤ tolerance zone radius for compliance.
GD&T Standards: True position is defined in ASME Y14.5 (GD&T standard). Common tolerances: ⌀ 0.005", ⌀ 0.010", ⌀ 0.020" (diameter tolerance). True position tolerance creates a circular tolerance zone (not square), allowing more usable tolerance than coordinate tolerancing.
Tips for Best Results
- Accurate Measurements: Use precise measurements from CMM or inspection equipment
- Correct Datum: Ensure measurements are relative to correct datum reference frame
- Check Tolerance Type: Verify whether tolerance is diameter (⌀) or radius (R)
- Verify Compliance: Ensure position deviation is within tolerance zone
- Use Standards: Follow ASME Y14.5 GD&T standards for true position interpretation
Frequently Asked Questions
How do I calculate true position deviation?
Position Deviation = √((Actual X - Nominal X)² + (Actual Y - Nominal Y)²). For example, Nominal (0, 0), Actual (0.001, 0.002): Deviation = √(0.001² + 0.002²) = √0.000005 = 0.0022". The calculator does this automatically.
What is true position tolerance?
True position tolerance (⌀) is a GD&T symbol that specifies the exact location of a feature. It creates a circular tolerance zone centered at nominal position. Tolerance zone radius = tolerance / 2 for diameter tolerance, or = tolerance for radius tolerance.
What is the difference between diameter and radius tolerance?
Diameter tolerance (⌀) creates a circular zone with radius = tolerance / 2. For example, ⌀ 0.010 creates a 0.005" radius zone. Radius tolerance (R) creates a circular zone with radius = tolerance. For example, R 0.005 creates a 0.005" radius zone. Diameter tolerance is more common.
How do I know if a part passes true position?
A part passes true position if Position Deviation ≤ Tolerance Zone (radius). For example, if deviation = 0.0022" and tolerance zone = 0.0025" (radius), then 0.0022 ≤ 0.0025 → Within Tolerance ✓. If deviation exceeds tolerance zone, the part fails true position inspection.
What are typical true position tolerances?
Typical true position tolerances: ⌀ 0.005" (0.127 mm) for precision parts, ⌀ 0.010" (0.254 mm) for standard parts, ⌀ 0.020" (0.508 mm) for general parts. Tolerances vary by part size, application, and manufacturing capability. Use appropriate tolerance for your application.