Estimate. it's a guideline it's not fact. Grab yourself an Ohmmeter and use that before you install (or a good Regulated mod that will read for you, though an Ohmmeter is cheaper and better).
When I was sticking with simple twisted wire I wanted something about .2Ω maybe slightly less. I realized 24g SS was getting me about .15Ω and 26gSS was getting me ~.23Ω iirc (been a while) so I went with a strand of each and it came out to .17Ω which worked well (and safe) enough for me.
Trial and Error is the key to vaping, sometimes you just end up throwing away a coil, big whoop wire is cheap and getting it just right is worth the effort, just give it a go, install, test and see what you get.
So plug into steam engine the two options for twisted and guestimate in between, I've found it'll not be right in between but a bit lower. Best I can do for ya.