Measures within tables

Hi all,

I'm getting an issue around using measures within a table, bear with me whilst I try to explain.

Table 1 : Product Codes

Table 2 : Customers

Table 3 : Sales

I want to know how many customers have ordered a specific product so I have created a measure works out the following:

Total Customers with Product / Total Customers (This is shown as a percentage)

Total customers seems to get filtered by each row of the table and therefore it works this out instead

Total Customers with Product / Total Customers (Filtered by product row)

Is there anyway I can stop Total Customers from being filtered and rather calculate as if all Customers were available even those who did not purchase the product?

Thanks,

J