conditional formatting - duplicate references

[gledister]

Imagine we have this column:

reference01
reference02
reference02
reference07
reference09
reference09
reference10

And what we want to get highlighted is only what is a duplicated reference...which means in this case the cells getting highlighted are going to be:

reference02
reference02
reference09
reference09

Thanks in advance!

 

[grizz]

assuming your numbers are in column B then conditional format / formula

=AND(ISNUMBER(B1), COUNTIF(B:B,B1)>1)

 

[ayazgreat]

or Try this
=COUNTIF($B$2:$B$100,B2)>1

 

[gledister]

thank you for both your alternatives!