Unique values based on multiple criteria

[mtalbot22]

I have a list of members with duplicate entries (different plots on an allotment). I need to find out how many unique members don't have an email address so that I know how much postage I have to buy to send them our newsletter. How do I use Unique to get the result? thanks in advance.

[#2]

@mtalbot22 

Try this formula:

=COUNTA(UNIQUE(FILTER(B2:B12, D2:D12="")))

[#3]

@mtalbot22 , I added the last name column to the formula inspired by @Hans Vogelaar :

=ROWS(UNIQUE(FILTER($B$2:$C$12,ISBLANK($D$2:$D$12))))