This is the number of people you expect would benefit from doing a particular option. If you’re using RICE in the context of sales, then it would be the number of customers you can potentially convert. If it’s in the context of maintenance or technical debt, it would be the number of people-hours saved from inconvenience.
Is a bounded score that measures the expected impact of an option, for instance, 1-to-10, where 1 is minimal impact, and 10 is a massive impact.
High confidence is 100%, Medium confidence is 80%, and low confidence is 50%. Anything lower should be considered a moonshot.
This is to get an idea of how much work is involved. This can be person-hours, or for large projects, person-months. Consistency in comparison is what matters.
Once you have all four: Reach, Impact, Confidence and Effort determined, you can then calculate the RICE score and end up with a definitive metric for comparison and determining order.