Free toolsTolerance stack-up
Tolerance stack-up calculator.
A one-dimensional stack-up for a gap or clearance. Get the worst-case and RSS ranges, check them against your requirement, and see which tolerance drives the result. Runs in your browser.
Results
Enter the loop, or try the sample: a bearing, spacer and retaining ring in a housing, with a required end clearance of 0.10 to 0.60 mm.
Nominal gap
Worst case
RSS, statistical
Contribution to variation
Worst case or RSS?
Both answer "will it fit?", with different assumptions about how parts vary.
- Worst case
- Adds every tolerance at its limit. If worst case passes, every assembly fits, guaranteed. It is the safe choice for small quantities, safety-critical fits and processes you don't control.
- RSS
- Root sum of squares: the square root of the sum of each half-tolerance squared. It predicts the range most assemblies fall in, because parts rarely sit at their limits all at once.
- When RSS is valid
- When each dimension varies independently, is roughly normal and centred, and its process is capable, with the tolerance equal to about ±3 standard deviations. Check capability with the Cpk calculator.
- Contribution
- Each tolerance's share of the RSS variance, its half-tolerance squared over the total. Tighten the biggest contributor first; tightening a small one changes almost nothing.
- Limits
- This is a one-dimensional stack. Geometric tolerances such as position, profile and perpendicularity, and 2D or 3D effects, need a fuller analysis.
Need the full stack checked?
A drawing and tolerance review marks up GD&T errors, ambiguous requirements and tolerances that drive cost, including the stacks that decide whether your assembly fits.