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Tolerance Stack-Up Calculator

List the dimensions that add to or subtract from a gap, give each its plus and minus tolerance, and read the nominal, the smallest and the largest value the chain can reach. Worst case, one dimension, calculated in your browser.

Nominal gap (mm)

6

Minimum 5.8 · maximum 6.5 (0.2 below, 0.5 above)

Largest contribution: dimension 2, 57.14 % of the 0.7 mm total spread.

  • Dimension 1

  • Dimension 2

Share of each dimension
  1. Dimension 1: 42.86 % (0.3 mm)
  2. Dimension 2: 57.14 % (0.4 mm)

One-dimensional worst case. Form, position, temperature and assembly effects are not included, and PASS or FAIL is not a statement about safety.

How it works

  1. Add one row per dimension: its nominal size, its plus tolerance and its minus tolerance (both as positive amounts).
  2. Choose + for a dimension that adds to the gap and − for one that subtracts from it.
  3. Read the nominal, minimum and maximum, and which dimension contributes most to the spread.
  4. Optionally type your lower and upper limits to get PASS or FAIL with the margins, then copy the result.

What people use it for

  • Checking a gap in an assembly

    A housing, two plates and a spacer: will the gap stay between the two limits whatever the parts do within tolerance?

  • Finding the dimension that costs the most

    See which part takes the largest share of the spread before you decide which tolerance to tighten.

  • Teaching and design reviews

    Show the arithmetic of a worst-case chain with asymmetric tolerances on one page.

Questions

How is the worst case calculated?
A dimension that adds contributes from (size − minus tolerance) to (size + plus tolerance). One that subtracts contributes from −(size + plus tolerance) to −(size − minus tolerance). The minimum is the sum of all the lower bounds and the maximum the sum of all the upper bounds.
Does it say whether the assembly will work?
No. It is a one-dimensional worst-case model: it ignores form, orientation and position tolerances, thermal effects and the way parts really sit against each other. PASS or FAIL only compares two intervals.
Why is worst case so wide?
It assumes every part is at its limit in the least favourable direction at the same time, which is rare. A statistical method gives a narrower range but needs assumptions about how the parts vary; this page does not make them.
Which unit should I use?
Any, as long as every row uses the same. The page only adds numbers: millimetres, inches or micrometres give the same arithmetic.