One way:

=ROUND((A2-A1)*24,0)

where A1 has your start date/time and A2 has your end date/time. Since
XL stores times as fractional days, multiplying integral plus fractional
days by 24 gives hours.

In article ,
Robin CSM002 <Robin wrote:

I need to calculate the difference in hours between two dates and times. For
example the difference in hours between 11:25 on 23/07/2004 and 18:00 on
06/08/2004? The dates and times have already been determined by the start and
end of a particular event. Thanks,