Use drop-down list to convert column from Lb to Kg

What I'd like to do is use a drop-down list that consists of two values, kg or lb, and when one is selected, have it run a calculation to convert a column (or multiple columns) from one to the other.  The column is now in pounds.  If the drop down is at "lb", then do nothing and use the value as-is.  If it changes to "kg", then multiply each value in the column by 0.45359237.

It sounds easy in my head but I'm sure that it isn't.  Any help would be appreciated.

(2) Answers