How to Calculate Tolerance Stack
What is Tolerance Stack?
Tolerance stack-up analysis determines cumulative effect of individual component tolerances on final assembly. Critical for assembly success.
Formula
Statistical method: total = √(sum of squares) — more realistic
Step-by-Step Guide
- 1Linear stack: total tolerance = sum of individual tolerances (worst case)
- 2Statistical method: total = √(sum of squares) — more realistic
- 3Design tolerances to achieve assembly fit requirements
Worked Examples
Input
Four parts each ±0.5mm, total stack tolerance requirement ±1.5mm
Result
Worst case stack = 2.0mm (exceeds), statistical = 1.0mm (passes)
Statistical justified
Common Mistakes to Avoid
- ✕Adding worst-case tolerances without justification
- ✕Ignoring correlation between tolerances
Frequently Asked Questions
When to use worst case vs. statistical?
Worst case for critical assemblies; statistical for high-volume production where cost matters.
How do you reduce stack tolerance?
Use fewer parts, use larger dimensions, or reduce individual component tolerances.
Ready to calculate? Try the free Tolerance Stack Calculator
Try it yourself →