But, since it’s not the case, 30F usually does the trick for me, so let’s go with that as my reference mark! It could also be useful to consider if my leaning bust was 3″ or more bigger than my standing or if my lying measurement was bigger than my standing, which could mean I’d need a FF or a G instead of F. The other 5 measurements become useful if, for example, there was a big difference between my snug and tight underbust measurements, which could mean I’d want to get a number between the two instead of rounding up the snug measurements. My snug underbust is 29″, which puts my band size at 30, and my standing bust is 36″, 36 – 29 = 7″, which comes out as an F cup in UK sizing, or a G cup in US sizing. However, some weirder places, like Victoria’s Secret, also use another measurement instead of the underbust, which I took just for fun: the perimeter passing at the height of the band in the back and over the bust, which comes up at 35″ for me.įirst, let’s calculate using the basic math I talked about in this post. Why did I take that many measurements? Because the most precise calculators can use all those 6 measurements, although most of them use only 2 measurements: snug underbust and standing bust. My measurements are 30″ loose underbust, 29″ snug underbust, 28″ tight underbust, 36″ standing bust, 38″ leaning bust, 36″ standing bust. Let’s take the time to measure exactly how misleading these calculators can be. However, when I went in store and told the fitter I measured myself as 30F or 30FF, she told me we’d need to try on some bras to confirm that, and there’s a good reason to this: online bra size calculators are VERY frequently misleading, even extremely misleading. But really, how did I come up with this result? I used an online calculator and then tried on bras in store, having a good idea of how bras are supposed to fit. I’ve mentioned multiple times so far that my ‘true’ bra size is 30F.