Ask HN: If asked for years of experience, how do you include part-time work?

Suppose you have some number of years of full-time experience in software development, and some other number of years where you were writing code part-time. Maybe you had a job that involved some dev work but some unrelated work as well. Or maybe you had an unrelated day job but did freelance dev work as a side hustle.

If you had to quantify that into a single number that represented your years of dev experience (e.g. on a job application), how would you come up with that number?