U.S. Imperial sizes: Imperial bar designations represent the bar diameter in fractions of 1⁄8 inch, such that #8 = 8⁄8 inch = 1 inch diameter. Area = (bar size/9)2 such that area of #8 = (8/9)2 = 0.79 in2. This applies to #8 bars and smaller. Bars higher in number have a slightly larger diameter than the one computed using the 1⁄8 inch formula.