Tolerance Stack-up Calculator
Add up to five dimensions in a chain to get the worst-case and statistical (RSS) tolerance stack-up for an assembly.
Enter your dimensions
Nominal size and symmetric ± tolerance for each dimension in the chain.
How this calculator works
Nominal total is a simple sum of every dimension in the chain. The two tolerance stack-up methods differ in how the individual ± tolerances combine:
Worst-case stacking sums every tolerance directly — the assembly's true physical limit if every part happened to land at its extreme simultaneously. RSS treats each tolerance as a statistical distribution and combines them geometrically, which is far more representative of what a real production batch will show.
Choosing a method
| Situation | Recommended method |
|---|---|
| Low volume, or safety-critical fit | Worst-case |
| High-volume production, normal distribution assumed | RSS (statistical) |
Frequently asked questions
Why is the RSS result always smaller than worst-case?
RSS assumes tolerances are independent random variables, so it's statistically unlikely all of them hit their extreme at once — the root-sum-square combination reflects that reduced probability, not a design allowance.
Can I mix asymmetric tolerances?
This calculator assumes symmetric ± tolerances for simplicity. For asymmetric tolerances, convert each to an equivalent symmetric value first, or calculate the upper and lower stack limits separately.