About Tolerance Stack Up Calculation
Tolerance stack up is a practical method for checking how part variations combine inside an assembly. Every manufactured part has a nominal dimension and an allowed deviation. When several dimensions form one chain, their small errors can increase, reduce, or cancel the final assembly size. This calculator helps you model that chain with clear assumptions.
Worst Case Review
The worst case method adds every harmful tolerance in the direction that creates the largest and smallest possible assembly values. It is conservative. It works well for safety, tooling, sealing, press fits, and any condition where every part could arrive at its limit. The result may be strict, but it shows the guaranteed envelope.
RSS and Sigma Review
The RSS method, short for root sum square, assumes independent variations. It squares each tolerance contribution, adds those squares, and takes the square root. This approach often matches stable production better than pure worst case. It should be used when processes are centered, controlled, and not strongly correlated.
The sigma option extends the RSS idea. You can state how many standard deviations each component tolerance represents. You can also choose the desired assembly coverage. This gives a statistical stack range. It is useful for estimating yield risk during design reviews and supplier discussions.
Direction and Targets
Use a positive direction when a component increases the measured assembly result. Use a negative direction when it reduces the result, such as a gap subtracting from a total length. Enter upper and lower tolerance magnitudes as positive numbers. The tool handles asymmetric tolerances and direction changes automatically.
Target limits help connect math to a real requirement. Add a minimum limit, a maximum limit, or both. The result section compares the selected method range with those limits. It also reports remaining margin or shortfall, so decisions are easier to review.
Engineering Notes
Tolerance stack up does not replace measurement plans. It supports them. Good data, stable machines, calibrated gauges, and clear drawings still matter. Review critical dimensions with manufacturing, quality, and suppliers before releasing a design.
This calculator is designed for early layouts, engineering checks, and documentation. Export the results to keep a record. Use the example table to understand the input style. Then replace those values with your own dimensions and tolerances. It supports concept, prototype, and release work.