I didn't leave out any commas. They really do recommend 75 sq ft per bird for a caged light breed. By caged, they mean that they will NOT be given access to any outside run. Example: An 8 x 10 cage is 80 square feet. The chart is on page 66 of Storey's Guide to Raising Chickens by Gail Damerow if you don't want to believe me.
If you want to use a cage for a short term period, and let's say you let the chicken free range when you are out, then you can use the following dimensions as a guide. A cage must be roomy enough for a chicken to stretch its neck, wings, and legs without touching the sides or top. Add 6" if you plan to install roosts. (Damerow 79)
1 bird 30"w x 24"d x 24"h
2 birds 27"w x 32"d x 24"h
3 birds 46"w x 32"d x 24"h