The floor mat contains a main piece with a number of first interlocking elements configured along a circumference of the main piece at intervals. Each first interlocking element contains a protrusion and a gap. The main piece also has a number of corner elements, each configured at a corner of the circumference. A hollow frame member is for the embedment of the main piece and has a number second interlocking elements matching the first interlocking elements along an inner circumference of the frame member. Each corner of the frame member has two perpendicular cuts end-to-end connected together and a slant cut running through a joint of the perpendicular cuts. As such, the floor mat can be pieced together in all directions, regardless of which side is up. The frame members can have their corners adjusted and fit on the main pieces to conceal their exposed interlocking elements.