I'm not exactly sure what you are referring to, but what you are describing seems similar to the Weighted Shortest Job First (WSJF) from the SAFe framework.
WSJF is a way to define the priority of features that need to be built and decide in what order to build them. It takes into account the fact that features that sit idle on the backlog with nobody working on them incur a certain cost (i.e. the cost of not having the feature available and usable), cost that can gather up if many items sit idle. To minimize this cost, the idea is to build the most important and shortest features first - to get "the biggest bang for the buck" so to speak - and only then move to the larger and less important features.
You can start reading about it here for example. To quote from that page:
At the end of the calculation of the WSJF, the features to be realized will be found in a very particular order:
- Features that are not complex but that have a high added value.
- Complex features that have a high added value.
- Features that are not complex with a lesser added value.
- Complex features with a lesser added value.
WSJF is just one of many prioritization techniques - sometimes you don't even need formulas if things are obvious on priorities/values - so again, not sure if this is what you were looking for.