Correlation Coefficient Calculator
Pearson's r, r², a scatter plot and a significance test, from two pasted columns.
- Free
- Runs in your browser
- No sign-up
One pair per line, as x, y. Paste two spreadsheet columns side by side and it just works.
No result yet
Paste at least three x, y pairs to get r, r² and the scatter plot.
Runs entirely in your browser. Your data is never uploaded.
How it works
What r actually tells you
Pearson's r runs from −1 to +1 and measures how tightly two variables move together in a straight line. Near +1 they rise together; near −1 one falls as the other rises; near 0 there is no linear pattern, which is not the same as no relationship at all.
Why r² matters more than r
Square r and you get the share of variance one variable explains in the other. An r of 0.7 sounds strong, but r² = 0.49 means barely half the variation is accounted for. r² is the number to quote when someone asks “how much does X explain Y?”
The two traps
First, correlation is not causation: a lurking third variable explains most surprising correlations. Second, r is fragile. One outlier can create or destroy it, and a strong curve can hide behind an r near zero. That is why this tool always draws the scatter, not just the number.
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