The basic idea
Cost per use divides the relevant cost by the number of realistic uses. It is most helpful when a high upfront price may be justified by frequent use, or when a cheap subscription becomes expensive because it is barely used. The denominator matters as much as the price.
Use realistic usage
Do not use the number of times you hope to use something. Use a normal scenario based on your recent behavior or a conservative plan. If the usage is uncertain, calculate low, normal and high-use cases. This shows whether the purchase only looks attractive under an optimistic assumption.
Choose the right cost
For a simple item, purchase price may be enough. For equipment, vehicles or memberships, include the recurring costs that are directly tied to having the option. If you expect to resell the item, net ownership cost can be more meaningful than the original sticker price.
Compare like with like
A rental fee may include maintenance or flexibility that ownership does not. A subscription may include a catalog of benefits rather than one use. Cost per use is a useful lens, not a complete verdict. Note meaningful differences in quality, access and convenience next to the number.
When it is most useful
Cost per use works well for clothing, tools, gym memberships, software, streaming, equipment and many household purchases. It is less useful when a product has important safety, reliability or emotional value that cannot be represented by usage frequency alone.
Use this method in a real comparison
Open a reviewed calculator, replace the example inputs with values that fit your situation, then change the assumptions that are most uncertain. A useful result should remain understandable even when the conclusion changes.