Pareto chart: paste your defects, get the ranking

Categories and counts in, ranked bars and the cumulative line out — with the vital few named, an "Other" bucket that always sorts last, and an honest warning when the distribution is flat and there is no dominant cause to attack.

Nothing you paste leaves this calculation. It is not stored, not logged and not sent anywhere else — the numbers are computed and returned, and that is all.

What a Pareto chart is for

Deciding what to work on. Bars ranked from largest to smallest, with a line showing the running cumulative percentage, so the question "which few causes account for most of the problem?" is answered by reading across rather than by arguing in a meeting.

The cumulative line is the point of the chart, not decoration. Without it you have a sorted bar chart, and a sorted bar chart does not tell you where to stop.

80/20 is a rule of thumb, not a law

Vilfredo Pareto observed that most of the land in Italy belonged to a small proportion of the population, and Joseph Juran generalised it into the "vital few and trivial many". It is a frequent pattern. It is not a property of nature, and your data is under no obligation to produce it.

A flat Pareto is a real and useful finding. If it takes nine of your twelve categories to reach eighty per cent, there is no dominant cause to attack, and choosing the tallest bar anyway means picking noise and spending a project on it. The correct response is usually that the categories are wrong — too fine, or split across a distinction that does not matter — or that the problem is genuinely systemic and needs a process change rather than a defect hunt.

The mistake that sends you to fix the wrong thing

Counting frequency when you should be counting cost.

The most frequent defect is very often not the most expensive one. Forty-seven scratches that polish out in seconds are a smaller problem than one contamination event that scraps a batch and triggers a customer notification — but on a Pareto by count, scratches tower over it and contamination is the last bar on the right.

Draw it twice. Once by count, once by cost — scrap value, rework minutes, warranty exposure, whatever the real unit is. When the two charts disagree, the cost one is the one that should set the agenda, and the disagreement itself is worth showing to whoever owns the budget.

Other things worth getting right

Categories must be mutually exclusive. If a part can be counted under two causes, the chart double-counts and the percentages mean nothing.
"Other" always goes last, however large it grows. An "Other" bar in the middle of the ranking is a broken Pareto. If it grows past the top few real categories, the roll-up threshold is hiding the problem rather than tidying it.
State the period. A Pareto is a snapshot with no time axis at all, so it cannot distinguish a category that is steadily worsening from one that had a single bad week. It ranks; it does not trend.

That last limitation is worth taking seriously. Once the Pareto has told you which category to attack, a control chart of that one category over time is what tells you whether it is getting worse, getting better, or has been stable all along — and whether the fix you applied actually did anything.

Questions people ask about this

How do I make a Pareto chart?

Count each cause over a stated period, rank them largest to smallest, and plot the counts as bars with the running cumulative percentage as a line on a second axis scaled nought to a hundred. Paste your categories above and this does all of it.

What is the 80/20 rule in a Pareto chart?

The observation that a small number of causes often account for most of the problem. It is a frequent pattern, not a law, and your data is under no obligation to produce it. If it takes nine of twelve categories to reach eighty per cent, that flat shape is itself the finding.

Should I count defects or cost?

Both, on two charts. The most frequent defect is very often not the most expensive one — forty scratches that polish out are a smaller problem than one contamination event that scraps a batch. Where the two charts disagree, the cost one should set the agenda, and the disagreement is worth showing to whoever owns the budget.

Where does the "Other" category go?

Last, always, however large it grows. An "Other" bar sitting in the middle of the ranking is a broken Pareto. If it grows past your top real categories, the roll-up threshold is hiding the problem rather than tidying the chart.

Can a Pareto chart show a trend?

No. It has no time axis at all, so it cannot distinguish a category that is steadily worsening from one that had a single bad week. Once it has told you which category to attack, chart that category over time to find out whether it is getting worse and whether your fix did anything.

Want this to keep itself up to date?

A calculator answers for the data you pasted. A control chart answers for the data your line produced this morning — limits frozen at a baseline you locked, rules evaluated on every new reading, an alert when one trips.

Start now See it on live data

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Everything else

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Nelson & Western Electric rules checker — Every run rule evaluated on your data, each violation named in plain English with what it usually indicates — a shift, a trend, tool wear, two machines mixed.
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X̄-s chart calculator — For subgroups big enough that the range wastes them. Limits from A₃, B₃ and B₄, sigma recovered with the c₄ correction, and the s chart read first because it decides whether the averages chart can be trusted.
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