I'm not sure what you are trying to find. "Total feet" is a length measurement, and so is a diameter. I'm also assuming you mean the diameter of a circle.
Other important length measurements of a circle are its radius (that's just half the diameter) and its circumference (that is pi times the diameter and pi is roughly 3.142).
Another important measurement is the area of a circle, but this is definitely not a length measurement and it is measured in square feet rather than feet. These are quite different things and shouldn't be confused because one depends on shape and the other doesn't really say anything about shape. If it is total square footage that you meant to ask, then you would use the formula A = pi r2, where r is the radius of the circle. If you measure the radius in feet, then the area is in square feet.
Hope this helps,
Stephen La Rocque.