After using Topper's suggestion, you can then work with just the duplicates
by using the autofilter (assumes you have a header row). Select the row with
your headers, click Data/Filter/Autofilter. You should see a drop arrow next
to the column w/Toppers formulae, click this arrow and select "Duplicate".

Turn off the filter the same way you turned it on.

"Damondism's" wrote:

I have a spreadsheet with thousands of invoice numbers, i need to identify
duplicate numbers within a specific column. I'm not great with excel,
lay-terms would be appreciated =)