This online calculator computes covariance between two discrete random variables. It also shows the expected value (mean) of each random variable. You can find formula used for calculation of covariance below the calculator.
Covariance between two discrete random variables
where E(X) is the mean of X, and E(Y) is the mean of Y.
If covariance is positive, then increase of one variable results in increase of another variable. If covariance is negative then increase of one variable results in decrease of another variable. Absolute value of covariance is usually normalized by dividing by the product of variables' standard deviations. This is so-called Pearson correlation coefficient.