Know-How Exchange : Research/Metrics

It depends on what information you have and how well you are able to track your CTAs. The simple answer is you take the total cost by medium and divide it by the number of sales that came from that medium.

How are you tracking your visitors/purchasers? If you know where they come from, this is half the battle. Not all media are the same - TV and billboard metrics are very hard to measure.

In a circumstance like this, it's usually best to put this sort of question on its head. Internet advertising is very fast and relatively inexpensive. That means you can tailor your message with a degree of accuracy. When you have tailored your message - that is when you use it in other media, because you already know it will work as well as it can. When you can't measure the effect of TV advertising as easily, make sure you don't need to. That's when you can leverage the information you gain from the internet - and your TV advertising will hit the mark and your millions won't be wasted.