Using Excel to calculate Two-Variable Correlation

• Correlation coefficient.
• Calculation using the Data Analysis Add-in.
• Calculation using the CORREL function.
  
• Covariances.

CORRELATION COEFFICIENT
The correlation coefficient between two series, say x and y, equals
  Covariance(x,y) / [Sqrt(Variance(x)) * Sqrt(Variance(y))]
where

• Covariance(x,y) is the sample covariance between x and y:  (1/(n-1)) × Σ _i (x_i - xbar)(y_i - ybar)
• Variance(x) is the sample variance of x: (1/(n-1)) × Σ _i (x_i - xbar)²
• Variance(x) is the sample variance of y: (1/(n-1)) × Σ _i (y_i - ybar)² 

CALCULATION USING THE DATA ANALYSIS ADD-IN (Lean how to activate it here)

The data used can be downloaded here here
We consider only two series, but we could do the same for more than two series.

• In the Data Group select the Data Analysis Add-in
• Select Correlation
• Fill out the Correlation dialog box as below

The Data, Click on Data Analysis (Data > Data Analysis) 

When you click data analysis,

When you click OK,

  The Result