Pareto Analysis Calculator
Pareto analysis ranks causes by contribution so effort goes where the return is. Its practical value in reliability work comes less from the 80/20 ratio itself and more from the discipline of ranking by consequence — usually downtime hours or cost, not raw failure count.
Formula
Worked example
Annual downtime by cause: seal leaks 210 h, bearing failures 145 h, control faults 60 h, coupling 35 h, other 50 h. Total 500 h.
- Seal leaks: 210/500 = 42.0%, cumulative 42.0%
- Bearings: 145/500 = 29.0%, cumulative 71.0%
- Controls: 60/500 = 12.0%, cumulative 83.0%
- Other: 50/500 = 10.0%, cumulative 93.0%
- Couplings: 35/500 = 7.0%, cumulative 100%
Two causes account for 71% of downtime and three account for 83%. Seals and bearings are where a reliability programme should start. Had this been ranked by failure count instead of downtime hours, a frequent but quickly-fixed nuisance fault could easily have displaced them at the top.
Common mistakes
- Ranking by failure count when the objective is to reduce downtime or cost. The two orderings often differ substantially.
- Letting an "other" bucket grow large enough to hide a real category.
- Running Pareto on categories defined at inconsistent levels — mixing a specific component with a whole subsystem.
- Treating the analysis as one-off. After the top cause is fixed, the ranking changes and the chart needs rebuilding.
Related tools
About Reliability Pro
Pareto Analyzer is part of a suite of 126 reliability, maintenance and quality engineering tools covering life data analysis, accelerated testing, system reliability, FMEA and root cause, SPC, and design for reliability. It runs in the browser and as native iOS and Android apps, so the same calculation is available at a desk or in front of the asset.