ROI is how every other investment in a company is measured, so why not advertising?

Unfortunately, if you're not selling all your products online, ROI can be very hard to calculate. The conundrum is spillover from online advertising to offline brick and mortar shopping. In these cases, the investment is online, but the return is attributed to other channels.

Online-only retailers who can capture the full effect of online advertising should by all means track ROI. To calculate ROI, sum-up all dollars coming in from sales attributed to your campaign and divide by campaign cost.

What if you only collect leads or applications and do not sell anything online? Then you can either calculate a "notional value" for each conversion (leads or applications), or track your investment on advertising by calculating the average cost per conversion.

From www.imediaconnection.com