Venn Diagram Set Evaluator — Free 2-3 Set Venn Tool

This tool evaluates Venn diagrams for two or three sets: it counts items only in A, only in B, in each pairwise overlap, in all three (for three sets), the union size, and the Jaccard similarity between A and B (intersection divided by union). You type items as comma-separated lists, and the tool draws overlapping circles and reports the counts. Venn diagrams turn abstract set operations into visible regions, which is why they survive from school mathematics into research: “how many participants are in both groups?” is a Venn question, and the diagram answers it without a formula.

How to use it

Type Set A items, comma-separated.
Type Set B items.
Optionally type Set C items.
Click Evaluate sets.
Read the region counts and the Jaccard similarity.

Worked example

Set A holds Ana, Bo, Cy, Dan; Set B holds Bo, Dan, Eli; Set C holds Dan, Eli, Fay. Only A counts 2 (Ana, Cy), A and B only counts 1 (Bo), all three counts 1 (Dan), and the union counts 6. The Jaccard similarity between A and B is the intersection (Bo, Dan = 2) divided by the union of A and B (Ana, Bo, Cy, Dan, Eli = 5), or 0.40 — the sets overlap substantially but are far from identical. A researcher comparing two recruitment sources reads that as: the sources overlap usefully, but neither replaces the other.

Honest limits

The tool handles two or three sets only; four or more sets cannot be drawn as simple overlapping circles and need other visualizations. Item matching is exact and case-sensitive after trimming, so “Ana” and “ana” count as different people — standardize names first with the Dirty String Standardizer. Jaccard similarity also ignores everything outside the two sets, so two small sets inside a huge population can look highly similar while sharing little of the population. For more than three sets, or for weighted and fuzzy membership, use dedicated set-visualization tools.

Who it is for

This tool is for students learning set operations, researchers comparing groups, cohorts, or sources, and anyone who needs overlap counts without drawing circles by hand. It is a counting aid with a picture, not a proof: the counts are exact for the lists you typed, and only as good as those lists.

Going further

Use Jaccard carefully when sets differ greatly in size: a small set fully inside a large one scores a low Jaccard (because the union is large) even though containment is perfect, so report the overlap coefficient too — intersection divided by the smaller set — when containment is the question. For recruitment or coverage questions, the more useful numbers are often the raw region counts (“how many only in A?”) rather than any single similarity index, because staffing and outreach decisions depend on counts of people, not on ratios. State which measure you report and why, so readers do not mistake a similarity score for a headcount. Venn counts become most persuasive when the sets themselves are defined in the report, not just in the tool. State the rule that put an item in a set — the inclusion criterion, the time window, the source list — because two readers who define the sets differently will count different overlaps and argue past each other. When sets come from different sources, also state how duplicates were matched: exact name, identifier, or fuzzy match, and what happened to near-matches that failed the rule. These definitions belong in the methods section, and the diagram belongs in the results, so a reader can move from definition to picture without guessing. A Venn diagram without set definitions is a pretty picture; with them, it is a reproducible count that another researcher can repeat and verify.

Embed this tool on your website — free

Copy the code below to add this working tool to your own page. A small credit link stays with it — that’s all we ask.