How much revenue is generated per amount spent on an advertising method.

The amount of revenue generated per dollar spent on a given advertising method.

The total revenue generated divided by the cost of your campaign. This is a very effective way of measuring the success of your campaign. In principle if the ROAS is below £1.00 your visitors failed to generate enough revenue to pay for the campaign, the ROAS amount needs to cover both your campaign costs and the cost of the goods sold.