Return on Ad Spend, or ROAS, is the percent a marketer gains from ad spend compared to what they have spent.
Calculation: Sale Amount / Spend = ROAS
Example: $200 in Sales / $100 Spend = 200% or 2X ROAS
By default, PCB's pixels (tracking codes) contain &saleamount= which is the parameter you can use to pass back to PCB what the end customer's spend on your products is.
In your UI, the Sale Amount can be found as a default column in your Dynamic Reporting and can also be found on the individual Conversion/Event level in the Clicks & Conversion Report.