In the ini.big file, it gives the length and width of the pitch in 16ths of a foot.
The number is 6450. So divide by 16 and you get the length in feet, which is 403feet.
There are roughly 3 feet in a yard, so divide by 3 and you get 134.3 yards
You can change the length by using a common.ini file, but the pitch graphics don't move (ie all of the white lines), but the goals, corner flags, linesmen and players all move accordingly and act correctly. If I could find the pitch lines file (and I will eventually) I can make it look like a pitch. But then, the penalty area is too small (because it reduces the whole length and width, when really you need to remove just the space between the centre circle and the penalty box), but I reckon you can solve this. The biggest problem is set pieces (ie corners and free kicks). The players not with the ball (ie those moving around and in the wall) ignore the new boundaries and use totally different ones (but no the original ones). Nobody will help me find the file for the graphics. I reckon you can change the actually penalty box size too, but the problem is the AI in the set pieces (at all other times, they work with the new boundaries).
Try it. Make a file called 'common.ini' in the main FIFA directory. Put in the lines :
FIELD_LENGTH=5520
FIELD_WIDTH=3648