Tolerance Stack-Up Calculator

Add multiple dimensions with plus/minus tolerances, then compare worst-case max/min envelope against root-sum-square (RSS) statistical stack-up for production assemblies.

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Measuring tools for stack-up checks

Calipers and shop tools for verifying assembled dimensions

Measure

Starrett Digital Caliper

Confirm nominals and actuals
Check stack results on the bench
Essential fab metrology

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Radius

SS Radius Gauge Set

Verify formed feature sizes
Catch bend-related stack errors
Quick shop inspection

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Snips

Malco M2006 Left Offset Snips

Trim blanks when stack forces rework
Sheet metal fab staple
Pairs with bend / gauge workflows

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Worst-case vs RSS tolerance stack-up

Worst-case adds every positive tolerance and subtracts every negative tolerance. Use it for safety-critical fits, hard tooling, and when you cannot accept statistical outliers.

RSS (root-sum-square) treats bilateral tolerances as independent random contributions: RSS = √(Σ tᵢ²). The statistical stack is narrower than worst-case and is common in production assemblies with centered processes.

MMC / LMC (brief)

Maximum material condition and least material condition change available tolerance when features of size interact with geometric controls. This calculator uses linear plus/minus stacks only — apply MMC/LMC bonus from the drawing separately. Decode the symbols and modifiers on the GD&T Symbol Reference Chart.

Fab tips

Assign directions carefully (gaps often subtract).
Don’t mix process capability assumptions with hard-gauge requirements.
Prove critical stacks with a physical mock-up when possible.

Frequently asked questions

Why is RSS smaller than worst-case?

RSS assumes not every dimension will hit its extreme at the same time. Worst-case assumes they all do.

Tolerance Stack-Up Calculator