cir·cum·fer·ence

– noun
1. the outer boundary, esp. of a circular area; perimeter.
2. the length of such a boundary.
3. the area within a bounding line.

pe·rim·e·ter

– noun
1. the border or outer boundary of a two-dimensional figure.
2. the length of such a boundary.
3. a line bounding or marking off an area.
4. the outermost limits.