Convert column letter to number

The first step is to construct a standard "A1" style reference using the column letter, by adding a "1" with concatenation:

B5&"1"

This results in a text string like "A1" which is passed into the INDIRECT function.

Next, the INDIRECT function transforms the text into a proper Excel reference and hands the result off to the COLUMN function.

Finally, the COLUMN function evaluates the reference and returns the column number for the reference.