Separate known uses from hoped-for uses

For an item already owned, divide the relevant cost by recorded uses. A hypothetical $60 tool used twelve times has an acquisition cost of $5 per use. This is a limited measure: it does not include maintenance, consumables or resale value unless you add those deliberately.

For a proposed purchase, the denominator is an estimate. Calling a $200 item “only $2 per use” assumes one hundred uses. Ask what makes that number plausible. A schedule of actual recurring tasks provides more evidence than a general intention to use the item frequently once it arrives.

Compare a range rather than one attractive number

Consider the same $200 item used twenty, fifty or one hundred times. The purchase cost per use would be $10, $4 or $2 respectively. Nothing about the item changed between those calculations; only the assumed use did. A range makes that dependency visible.

Check alternatives on the same basis. Borrowing or renting may involve access costs and inconvenience, while ownership may require storage and maintenance. Do not compare a fully costed rental with a purchase that includes only the sticker price, or the reverse.

Include the value of the task

A low cost per use does not establish that the activity is worthwhile. Conversely, an infrequently used item may serve an important function that a frequency measure misses. The calculation is one way to understand cost, not a complete judgement about need or suitability.

Avoid increasing use merely to justify a past purchase. Money already spent does not become recoverable because you invent more occasions to use the item. The useful question is whether ownership continues to serve a real task and what future costs follow from keeping it.

Use the number as a question

Before buying, write the expected cost, likely use range and the alternative being considered. After a suitable period, compare the assumptions with actual use. A substantial difference can improve the next decision without turning the record into a judgement of personal worth.

Cost per use works best when the calculation stays honest about its boundaries. It can challenge a sales pitch or a personal assumption, but it should not be used to manufacture certainty about future behaviour.