The most practical way to calculate your ROI is to use a custom-built tool. Conectio has a comprehensive yet simple calculator that produces excellent results.
To calculate straight ROI manually, use this formula:
(Total sales - total spend) / total spend
So, if your campaign generated $1000 in sales, and you spent $700 on advertising, it would look something like this:
1000-700 = 300
Then, 300/700 = 0.47, or 47% ROI.
Return on ad spend (ROAS) is a more accurate measure of performance, in this case, but ROI is still critical to get a holistic idea of your marketing efforts.