Tolerance Stack-Up Calculator

How to do a tolerance stack-up

1. List each dimension in the chain on its own line, such as 25 ± 0.1, or 25 +0.1 -0.05 for unequal tolerances.
2. Start a line with - for a dimension that is subtracted, such as a gap measured the other way.
3. Compare the worst-case range with the RSS (statistical) tolerance.

Frequently asked questions

Worst case or RSS?

Worst case assumes every part is at its limit at once, which is safe but strict. RSS assumes the variations are independent and random, which is more realistic for many parts in a chain.

How is the RSS tolerance worked out?

The square root of the sum of the squared tolerances. ±0.1, ±0.1 and ±0.2 give about ±0.245, against ±0.4 worst case.

What about unequal tolerances?

A dimension such as 25 +0.1 −0.05 has different upper and lower limits, so the upper and lower ends of the stack are worked out separately.