How many square feet are in a football field?

Answer

including end zones - 57,600 (160 W X 360 L)
without end zones - 48,000 (160 W X 300 L)  

Answer

An American football field is 120 yards long (360 feet) by 53 1/3 yards wide (160 feet). 360 x 160 = 57,600.


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To add to this:

According to the NFL : rulebook/beginnersguidetofootball
The football field is 100 yards long and 53 yards wide.

There are two endzones that are 10 yards.
There are 3 feet in a yard
So:

Without endzones: (100 X 3) X (53 X 3) = 300 X 159 = 47700
With Endzones (plus 10 yards on each end) (120 X 3) X (53*3) = 360 X 159 = 57240