About this tolerance stackup calculator
Tolerance stackup calculator
Tolerance Stackup Calculator - Worst Case & RSS Analysis
A practical tolerance stackup calculator for checking dimensional variation, assembly limits, and fit risk with worst-case and RSS methods.
Use this tolerance stackup calculator to check how drawing tolerances accumulate into a final gap, clearance, interference, position error, or assembly fit risk. It is designed for practical design reviews where a nominal fit is not enough and the team needs to see worst-case limits, statistical RSS behavior, and the contributors that drive the stack.
Common engineering uses
Common engineering uses
- 1D linear dimension chains for gaps, end play, shims, spacers, covers, and assembly offsets.
- Clearance hole, tapped hole, press fit, datum shift, thread engagement, and padeye-shackle fit checks.
- Early tolerance allocation work before releasing drawings, inspection plans, or manufacturing changes.
Outputs to review
Outputs to review
- Worst-case high and low limits for guaranteed assembly checks.
- RSS results for independent, random, centered contributors when process data supports statistical treatment.
- Contributor ranking, warnings, saved projects, and report-ready engineering notes.
How to use this tool
How to use this tool
- Enter nominal dimensions and tolerance values.
- Compare worst-case and statistical stackup results.
- Review assumptions, examples, and calculation limits.
- Save or revisit calculation projects from your account.
How to use the result
Choose the module that matches the drawing problem, then enter nominal dimensions and tolerances exactly as they appear in the functional loop. Review the worst-case result first when guaranteed fit matters. Use RSS only when the contributors are independent, reasonably centered, and supported by manufacturing capability or inspection data.
Assumptions, limitations, and formulas
Assumptions
Each contributor in the tolerance loop is entered in one consistent unit system.
Worst-case analysis assumes every tolerance contributor can sit at its most unfavorable limit at the same time.
RSS analysis assumes contributors are independent, random, and reasonably centered around nominal values.
Limitations
The calculator is an engineering aid and does not replace drawing review, GD&T interpretation, inspection planning, or qualified design approval.
RSS results should not be used for guaranteed fit unless the manufacturing process has supporting capability data.
Assembly effects such as distortion, thermal growth, elastic deformation, and process shift must be checked separately when they are significant.
Formula notes
Worst-case stackup adds signed tolerance extremes arithmetically along the functional loop.
RSS stackup combines independent contributors using the square root of the sum of squared tolerances.
Clearance, datum-shift, press-fit, thread-engagement, and padeye-shackle modules apply the same loop logic to their specific geometry.
Common questions
What is a tolerance stackup?
A tolerance stackup is the accumulated dimensional variation across parts in an assembly. Even when every individual part is within tolerance, the combined stack can create clearance, interference, alignment, or end-play problems.
What is the difference between worst-case and RSS tolerance stackup?
Worst-case analysis adds the most unfavorable limits arithmetically and is the conservative fit check. RSS analysis combines independent variation statistically, so it is useful when manufacturing variation is random, centered, and supported by process data.
Which tolerance stackup modules are included?
The calculator covers 1D linear chains, rectangular and circular clearance-hole stackups, tapped-hole stackups, press-fit shaft and bore checks, bolt head or washer pull-through, GD&T datum shift budget, thread engagement depth, and padeye-to-shackle pin fit.
When should I use worst-case tolerance analysis?
Use worst-case tolerance analysis when every acceptable part must assemble without relying on statistical averaging, especially for low-volume builds, safety-critical fit checks, or early design gates.
When is RSS tolerance analysis appropriate?
Use RSS tolerance analysis only when contributors are independent, random, and reasonably centered. It is helpful for estimating production yield, but it should not replace worst-case review where guaranteed fit is required.