When I measure my foot it is roughly 11 inches in length.
11 inches comes out to about 27.94 cm.
Would I be more suited for a 27.5 boot, or a 28? How do you typically advise boot buyers when they have a foot size such as this?
You look at their foot to see what boot will fit their foot the best, along with a few other options, then have them try them on while gentle assuring them that "yes, I know your toe is touching the front of the boot that's what we want... yes, they should feel a little tighter than the flip-flops you were wearing when you walked in... no, before you take the boot off because it's "too small" let's try buckling it, OK...work with me here a little..."
Measuring the length of your foot is pretty meaningless in the fitting process. Honestly, you can take the size shoe you normally wear and subtract 1 size for a comfortable performance fit and 2 sizes for an aggressive performance fit. It's at least as accurate as measuring your foot with a ruler then posting on the internet.