The physical dimension for pitch is based on the number of players that would be playing on that pitch. Also, there is not really a fixed measurement that a pitch must-have, just that there are the minimum and maximum dimensions for the pitch.
A pitch can be measured for a 5-a-side, 7 a-side, 9 a-side, or the popular 11 a-side. I will be talking more about the dimension for the 11 a-side, being the most common one. The answer to this is not a straightforward answer as different factors make the determinant of exactly how the pitch should be.
A major factor is the age factor. For a football pitch for under 14 players, the dimension in length to width would be 82.2m (90 yards) to 50.2m (55 yards). For under 16, the dimension would be 91.4m (100 yards) to 54.8m (60 yards). For the 18 and above, the dimension is 100.5m (110 yards) to 64m (70 yards). Lastly, we have the 12 yards and 18 yards box.