Wrench Sizes; How Many Inches Equal 8mm?

1-inch = 25.4 mm
 
8mm x 1-in / 25.4mm = 0.3149597-inch
 
5/16 = .3125 which may be close enough
 
 

1"=25.4 (millimeters), 1"divided by 25.4(mm)=.0394 (times into a inch),25.4 x.0394=1(whole or 1") ,1(mm)=.0394 (of an inch) , 8(mm) x.0394=.3152(of a inch), .3152 (of a inch) x16(ths of a inch)=5.0432(16ths of a inch) or rounding up to the whole number  =5, 5/16"

5/16 th