The calculation is straightforward. To compute the ROI ratio, you use the formula: ROI = (Net Profit / Cost of Investment) x 100 For instance, if you spent $1,000 on an email marketing campaign and earned $4,500 in revenue, your net profit would be $3,500. Plugging these numbers into the formula gives: ROI = ($3,500 / $1,000) x 100 = 350% The ROI percentage can then be converted to the 4.5:1 ratio by dividing the percentage by 100 and adding 1 (as it represents the total return including the initial investment).