Engineering · Calculator
Tolerance stack-up calculator.
Add up to 12 stacked dimensions, each with its own ± tolerance, and see the worst-case and statistical (RSS) accumulated tolerance. Use it for assembly clearance planning, datum-stack analysis, and detecting when a tight final tolerance is being driven by accumulated mid-stack values.
Stack chain
Add dimensions to the stack.
Enter mean dimension and ± tolerance for each link. Use a negative mean for subtractive directions (e.g., when measuring back from one face to another). Up to 12 rows.
Result
Worst-case adds tolerances arithmetically. RSS uses statistical accumulation (assumes each tolerance is independent and normally distributed at ±3σ). RSS is appropriate for assemblies where component variation is genuinely random; worst-case is the safer choice when correlation is possible.
When to use which
Worst-case vs RSS.
- Worst-case for safety-critical: use when assembly failure has high consequences (aerospace, medical, defense). Pessimistic — assumes all tolerances stack against you simultaneously.
- RSS for production statistical: assumes random independent variation across many parts. Realistic for high-volume production where mean-of-mean centering is enforced through SPC.
- RSS reduction depends on the chain: for a 6-link chain with equal tolerances, RSS gives √6 = 2.45× single tolerance, vs worst-case 6× single tolerance. Drawing tolerances alone do not establish a ±3σ process distribution.
- Don't mix in correlated dimensions: if two links come off the same datum and shift together, treat them as one combined link, not two independent ones.
For tolerance-cost trade-offs, see tolerance vs cost ladder.
Keep exploring
Related tools & references
Standard tolerance grades that feed each stack term.
Clearance and interference fits for mating features.
Check positional tolerance for the hole patterns in your stack.
How tighter limits in the stack drive cost.
Translate drawing callouts into stack inputs.
Have a part that needs these tolerances held?
Tell us about your part and we'll get back to you promptly. Aerospace, medical, defense, and semiconductor production work welcome.Email CAD models and drawings to sales@digitalmachine.com, including ITAR, EAR, CUI and AS9100 work. Keep controlled technical data out of web forms.
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