Use the CORREL function
Enter the formula: =CORREL(array1,array2)
Select the first range of data for array1
Select the second range of data for array2
Press Enter
Use the PEARSON function if preferred: =PEARSON(array1,array2)
Use the Data Analysis ToolPak
Go to the Data tab
Click Data Analysis
Select Correlation
Choose the input range
Check Labels in first row if needed
Choose an output range
Click OK