ROI means Return Of Investment, is usually expressed as a percentage and used to describe the profitability of an investment.
The basic formular for ROI is: ROI (%) = Profit / Investment * 100
If your ROI is 1 (or 100%) it means spend equals revenue (1:1 ratio). You didn’t lose money, but also didn’t make profit.
A negative ROI means that your investment was higher than your profit and that you lost money.
Which ratio you consider “good” depends on many, many factors. But I think in general it’s save to say that every ROI above 1 or 100% is at least positive.
If you have all the data it’s very simple, just use this formula: ROI = Profit / Investment * 100. You can also use this calculator.
The Formular for ROI is ROI = Profit / Investment * 100. So, if you want to increase ROI you need to get higher profit with same investment or same profit with lower investment.