I don't have access to a track for workouts but I have a track workout coming up. Would running the perimeter of a soccer field be 400m?
No. Soccer fields fit inside of tracks.
Interesting post on Tracktalk about this last spring. Poster left detailed instructions of how to lay out a grass track using things that could be found at the Hardware store. There are diagrams to help promote layout efficiency.
The poster's idea was to fit all the tools in a backpack and call it Track in a Pack.
If it's an Olympic-size soccer field, you'd be 10-80m short.
If it's a normal high-school-size soccer field, it would be a quite bit shorter, since the distance across the short side of a soccer field is the diameter of the circumference of the curve of the track. Circumference = 2πr but since the curve on a track is a semicircle its circumference is πr, where r is half the width of the soccer field. The curve is 100m, so 100m = πr and that means that r = ~33m. If you run as far to the outside of the field as possible (meaning that the length of the field would be ~100m), the distance for one lap around the field would be ~266m. This also means that if you run a lap and a half around the field, it would be ~400m.
For me, 400 meters was the distance around the field track. This track has a larger circumference