Tolerance stack-up calculator
Add up the nominal dimensions and tolerances of a three-part stack, both worst case and statistical (RSS).
How it is calculated
Worst case: sum of tolerances. RSS: √(t1² + t2² + t3²). Nominal total = sum of nominals (linear chain).
Worked example
10 ± 0.1, 20 ± 0.2, 5 ± 0.05: total 35 mm, worst case ± 0.35 mm, RSS ± 0.229 mm.
Steps
- List each part in the chain with its nominal and tolerance.
- Read the worst-case tolerance for a strict limit.
- Use RSS for high-volume parts with a process capability known.
Frequently asked questions
When to use worst case?
For safety-critical or low-volume parts where no scrap is acceptable.
When to use RSS?
For high-volume assemblies with stable processes. It assumes normal distribution and no bias.
Does this handle more than three parts?
This version handles three. Add rows by adding the same pattern in the calculator code.
References
Worst-case and RSS stack-up methods (ASME Y14.5 and common DFM practice).
Estimates for information only. Verify critical values with a qualified engineer or your supplier standards.