What is tolerance stack-up analysis?

Tolerance stack-up analysis determines the cumulative effect of individual part tolerances on an assembly's overall dimension. It helps engineers ensure that assembled parts will fit and function correctly.

What is the difference between worst-case and RSS?

Worst-case assumes all tolerances are at their extreme limits simultaneously (100% parts pass). RSS (Root Sum of Squares) is statistical and assumes a normal distribution — it gives a smaller total tolerance (typically 99.73% confidence at 3σ) but is more realistic for production.

When should I use worst-case vs RSS?

Use worst-case for safety-critical applications, small production runs, or when 100% interchangeability is required. Use RSS for high-volume production where statistical methods are valid and some small rejection rate is acceptable.

What does bilateral tolerance mean?

Bilateral tolerance is expressed as a nominal dimension ± tolerance (e.g., 50 ± 0.1 mm). The tolerance is distributed equally on both sides of the nominal value. Unilateral tolerance goes in only one direction.

How many dimensions can I stack?

This calculator supports up to 8 dimensions in a linear stack. For more complex 2D/3D tolerance analysis, specialized software (like 3DCS or CETOL) is typically used.

Free Engineering Tool

Tolerance Stack Analysis Calculator

Enter up to 8 dimensions with bilateral tolerances. Calculate worst-case and RSS (statistical) total tolerance for your assembly.

Worst-CaseRSS (3σ)Up to 8 Dims

Stack-Up Results

Nominal Assembly Dimension

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Worst-Case Tolerance

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RSS Tolerance (3σ)

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WC Range

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RSS Range (99.73%)

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Worst-Case Method

The worst-case method assumes all dimensions are at their extreme limits simultaneously:

RSS (Root Sum of Squares) Method

The statistical method assumes dimensions follow a normal distribution (3σ process):

Tip: RSS gives a tighter total tolerance, but assumes 99.73% (3σ) confidence. Use worst-case when 100% interchangeability is required.

Tolerance Stack Analysis Calculator | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026

Stack-Up Results

Worst-Case Method

RSS (Root Sum of Squares) Method