Pearson Correlation Calculator

Measures the strength and direction of a straight-line relationship, from −1 to 1.

Pearson r

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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.

Values read in each list —

r² —

p-value, two-sided —

95% confidence interval —

t statistic —

Degrees of freedom —

Reading this —

The formula

r = Σ(x − x̄)(y − ȳ) ÷ √(Σ(x − x̄)² × Σ(y − ȳ)²) t = r√(n − 2) ÷ √(1 − r²)

The interval uses Fisher’s z transform. The p-value and the interval both assume roughly normal data.

One extreme point can dominate r. If you have outliers or a curved but steady relationship, Spearman’s rank correlation is often the better choice.

What is a strong correlation?

It depends on the field. r = 0.5 can be a strong result in social research and a poor one in a physics measurement.

What is a worked example?

For X = 1, 2, 3, 4, 5 and Y = 2, 4, 5, 4, 5, r = 0.7746.