First, you need to decide how you enter your duration values. Remember,
1,30 minutes is not the same as
1 minute and 30 seconds - it is
1 minute and 18 seconds, since a minute is 60 seconds.
If you insist on a format of
minutes,seconds, you'll need a formula to parse this as a duration. I suggest using a regular expression. This formula will split a
minutes,seconds value in
A2 into two cells
Having that, we can calculate a decimal number of minutes (so that
1 minute and 30 seconds is displayed as
1.5 minutes). Enter this formula in
Now that we know that
1 minute, 30 seconds equals
1.5 minutes, it is easy to calculate the charge. Let's put the minute charge in cell
G1, then, in
... which should display as
See the example spreadsheet I have set up.
Note: Instead of parsing a
minutes,seconds string with regex, you might have some luck experimenting with Format → Number → More formats, and using the Elapsed minutes/Elapsed seconds placeholders, but the feature seems buggy and non-obvious.