Energy Return on Investment (EROI) is a formula for measuring the overall efficiency of any product or service, including your website. It is a measure of how efficiently a product or service produces sales or helps customers recognize your business.It’s easy to create numbers that look good, but it’s also important to understand what you’re looking at because they won’t necessarily hold true in reality. You need to be able to determine what your EROI is so you can guide clients, customers and advertisers in the right direction.