Exchange a number for a letter forumla

Hi guys,

This has been driving me crazy and after several hours of following tutorials I am at my wits end. Can one of you genius Excel folk help me out?

I have a sheet which calculates payment amounts.

Column titles:
Hours | Rate of Pay | Total

In the hours column usually the entries consist of numbers and everything works fine. However when an employee is on holiday they are still paid.

What I want to do is be able to enter the letter "H" for one of the entries in the hours column. The sheet to translate this as 2 hours.

H=2 x rate of pay = total

I cannot for the life of me get the correct formula to in order to achieve this. I don't particularly want to use a macro for this and others have suggested the "COUNTIF" function.

Anyone any ideas?
Sorry if I haven't explained this too well!