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Correlation Calculator: Pearson r, r Squared and Covariance

Pearson r, r squared and covariance for two paired lists.

Statistics Calculators Free, no sign-up Runs in your browser

The two lists must be the same length.

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Correlation r
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r squared
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Strength
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Covariance
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Pairs
StatisticXY
Correlation measures how closely two sets move together in a straight line. It is not evidence that one causes the other, it cannot see a curved relationship, and a single extreme point can create or destroy it.

About the Correlation Coefficient Calculator

Correlation Coefficient Calculator computes Pearson's r for two paired lists, along with r squared and the covariance. r runs from -1 to +1: plus one is a perfect upward straight line, minus one a perfect downward one, and zero no linear relationship at all.

r squared is the more interpretable number. It is the share of the variation in one variable accounted for by the straight-line relationship with the other, so an r of 0.77 gives an r squared of 0.6, meaning about sixty per cent of the variation is explained and forty per cent is not. Reporting r alone tends to overstate how much a relationship explains.

Three limitations are worth stating every time. Correlation does not imply causation. It only detects straight-line relationships, so a strong curved relationship can show an r near zero. And it is sensitive to outliers: one extreme point among twenty can create an apparent correlation or destroy a real one, which is why plotting the data matters as much as calculating the coefficient.

The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.

Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.

Looking for something this does not cover? FreeToolStation.com is a second collection of the same kind of everyday tools, and it is worth a look if correlation coefficient calculator is only part of what you are working on.

How to use the Correlation Coefficient Calculator

  1. Choose treat the data asThe fields below change to match what you pick, so only the figures that matter to your case are asked for.
  2. Enter x values and y valuesDecimals are fine, and thousands separators are accepted and ignored.
  3. Read the correlation r, r squared and strengthThe figures update as you type. The Calculate button is there if you would rather press something, but nothing waits for it.
  4. Copy or check the resultCopy the summary with the copy button, or open the table to check it row by row.

Features

  • Shows correlation r, r squared, strength, covariance and pairs together, so you are not running it twice
  • A results table you can read across
  • Updates as you type, with no button to press and no page reload
  • Copy the result in one click
  • Free, no sign-up, and it runs entirely in your browser

Who uses this tool

The correlation coefficient calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

  • Measuring how closely two variables move together
  • Reporting r and r squared for a dissertation
  • Checking a correlation claimed in an article
  • Deciding whether a linear model is worth fitting

Frequently asked questions

What counts as a strong correlation?

Conventionally above 0.7 in absolute value is strong and above 0.9 very strong, but it depends entirely on the field. In physics 0.9 might be poor; in social science 0.5 can be notable.

Does correlation prove causation?

No. It means the two move together in your data. The cause could run either way, or both could follow something else entirely.

What does a correlation of zero mean?

No linear relationship. There may still be a strong non-linear one, which is why a scatter plot should always accompany the number.

If the correlation coefficient calculator is not quite what you need, these other free tools solve closely related problems, and there are 13 more in statistics calculators.

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Checked and rebuilt on 2026-10-14. The method this calculator uses is described in the section above, and corrections go through the contact page.