[mjevans]

3/8ths is 0.375 while 1/3rd is 0.333~ so it's even bigger while still larger than 1/4th (0.250), without being that much bigger.

3/8ths is a pretty good marketing point since all the numbers are bigger and it should be intuitive, plus you can more easily see that it's also 50% bigger than 1/4th => 2/8ths. The harder sell is the 'double whatever' being equal to 3 patties of the competitor.