How To Measure
When buying a toilet seat, SIZE is very important.
Measure your toilet to determine whether your bowl is:
                                                                       elongated (approximately 18 1/2" long) 
round or regular (approximately 16 1/2" long)
Measure from center of bowl to center of the hinge post holes.  In the United States, the standard distance between hinge post holes is 5 1/2".