Men's sizes cluster between 8 and 12. Inside diameters: Size 8 = 18.1mm · Size 8.5 = 18.5mm · Size 9 = 19mm · Size 9.5 = 19.4mm · Size 10 = 19.8mm · Size 10.5 = 20.2mm · Size 11 = 20.6mm · Size 11.5 = 21mm · Size 12 = 21.4mm.
Sizing a wide band
Most men's bands run 6mm+ wide, which wears roughly a quarter-size tight — measure with a wide sizer or order up. Knuckles count too: if the knuckle is a half-size larger than the finger base, fit the knuckle and let the band spin slightly.
Tungsten and meteorite bands cannot be resized — confirm with a free sizer before ordering. Gold, platinum, and tantalum can.