Correlation Calculator
Pearson's r, and the r² that deflates it.
Work out Correlation. Pearson's r, and the r² that deflates it. Free, with no account and nothing to download.
Correlation (r)
0.91652
very strong positive · r² = 0.84
r² is the share of variation in y explained by x, and it is literally r squared — which is where over-claiming usually starts. A correlation of 0.92 sounds very strong, but it accounts for only 84% of the variation. The other 16% is something else. And none of this establishes causation: a strong fit is equally consistent with x causing y, y causing x, or a third factor driving both.
How the Correlation Calculator works
Pearson's r measures how well two variables move together, from −1 to +1. The number worth attending to is r², the share of variation actually explained — a correlation of 0.7 sounds strong but accounts for under half the variation.
Also known as: pearson correlation coefficient calculator · r value calculator · correlation coefficient formula · how to calculate correlation
r against r squared
Pearson's r runs from −1 to +1 and measures how tightly two variables track a straight line. r² is that number squared, and it is the share of variation in one variable that the other explains.
The gap between them is where over-claiming starts. A correlation of 0.7 sounds strong, and it is — but it accounts for 49% of the variation. More than half is something else.
What it cannot tell you
Correlation is symmetric and causation is not, so a strong r is equally consistent with x causing y, y causing x, or a third factor driving both.
It also only measures linear relationships. A perfect parabola can have a correlation near zero, because the rising and falling halves cancel — so a low r means no linear relationship, not no relationship.
And it is sensitive to outliers, particularly in small samples. A single extreme point can create or destroy an apparent correlation, which is why plotting the data matters more than computing the coefficient.
Frequently asked questions
What is a correlation coefficient?
A measure from −1 to +1 of how closely two variables move together. +1 is a perfect rising line, −1 a perfect falling one, and 0 no linear relationship at all.
What is the difference between r and r²?
r² is r squared, and it is the share of variation in one variable explained by the other. r = 0.7 gives r² = 0.49 — under half, despite sounding strong.
Does correlation prove causation?
No. A strong correlation is equally consistent with x causing y, y causing x, or a third factor driving both. Establishing causation needs an experiment or a strong design argument.
What counts as a strong correlation?
It depends entirely on the field. Above 0.8 is strong in most contexts, but physics expects far higher and social science routinely works with far lower.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
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