The Tolerance Stack-Up Calculator performs a simple worst-case linear stack for dimensions written as nominal ± tolerance. It is useful for an initial assembly check before applying a more detailed GD&T or statistical tolerance analysis.
What is tolerance stack-up?
When several part dimensions contribute to one functional gap, length or position, their individual variations accumulate. A worst-case stack assumes every contributing dimension simultaneously moves toward the same limiting condition. This is conservative and easy to audit.
How to use it
Enter dimensions separated by commas, for example 50±0.10, 25±0.05, 10±0.02. The calculator reports the nominal total, lower limit, upper limit and total tolerance band.
Worked example
For 50±0.10 mm + 25±0.05 mm + 10±0.02 mm, the nominal stack is 85 mm. The total worst-case tolerance is ±0.17 mm, giving a range of 84.83 to 85.17 mm. If the assembly requirement is tighter than this range, the drawing or datum scheme needs review.
Worst-case versus statistical stack-up
Worst-case analysis assumes all dimensions reach their unfavorable limits together. Statistical methods can predict a smaller distribution when manufacturing variation is controlled and independent assumptions are justified. Do not use statistical tolerance allocation simply to make a design pass; the manufacturing process and inspection strategy must support the assumptions.
Where GD&T matters
A simple linear stack is not enough when the functional requirement depends on true position, orientation, profile, runout or datum relationships. In those cases, build the stack around the functional datum reference frame and the actual assembly condition.
Common mistakes
- Adding tolerances without first defining the functional requirement.
- Mixing dimensions that do not belong to the same variation path.
- Ignoring assembly direction and datum structure.
- Applying unnecessarily tight tolerances to every dimension.
- Using a worst-case result when a validated statistical approach is actually required.
Related guides
Tolerance stack-up for a mechanical assembly · Choosing engineering tolerances · Mechanical design datums · Engineering drawing basics
Standards
For dimensional fits and tolerances, consult the applicable standards such as ISO 286 and ASME Y14.5 rather than relying on generic tolerance values.