The capacity of exits and access facilities shall be measured in units of width of twenty-two inches, and the number of persons per unit of width shall be determined by the occupancy group classification and type of exit as listed in table 6-1. Fractions of a unit of width less than twelve inches shall not be credited. Where twelve inches or more are added to one or more full units of width, one-half unit of width may be credited. Where computations of total required width give fractional results, the next larger integral number of exit units or integral number plus one-half, shall be used. A fraction less than one-half may be neglected in cases where such fraction constitutes less than ten per cent of the total required number of units. Notwithstanding any of the above computations, no exit or access facility shall be narrower than the minimum width requirements specified in table 6-1, or elsewhere in this code.