so an update to the above... my wife got her size 5, way too large. i tried her 5 (40mm) on my 44mm watch since the length should be the same... its still too loose. it mainly stays in place where i normally wear the watch but arm movements will cause it to slowly migrate down to my wrist bone, i certainly couldn't wear it running for example. the fit might be what some like, but to me it remains too loose for a smartwatch with optical HR and blood oxygen sensors that depend on a reasonably tight fit. SOOOO... for me, size 6 was way too large (this was what the paper tool suggested) and size 5 just was just a bit too large, but maybe ok for some if they liked a slightly loose fit.
i just online ordered a size 4 44mm band for me and both size 3&4 bands for my wife... i'll return the one she likes less, as of now local apple stores ARE getting daily resupplies but color and sizes are hit or miss so i'm not driving 30 minutes out there over and over again to get a silly band.
sorry to say but apple brought this on themselves, i suppose my new S6, new iPhone 12 Pros later this year and all the other stuff I constantly buy from them (plus the 90%+ profit margin on these rubber bands) will have to make up for all the trial and error. ugh, i wonder if apple will keep selling these in the long term, I guess at some point we will all know our "size."