July 3, 2012
The "height" of the toilet seat is measured from the front of the ring to the center point of the hinge bolt hole. If you measured from the front of the seat to the very end of the hinge, your measurement will be slightly longer than what is normally measured.
In general, seats come in two sizes. There is a visual size guide that can help on Home Depot's product page. Click on "More Info" and the "Instructions / Assembly" PDF.
Often you measure the bowl from the center point of the bolt holes in the back to the front tip of the bowl. If that size is in the 16.5" range, we consider that a "Round" size bowl. If it's 18.5", it's considered "Elongated".
You should be confident buying a seat that's then Round or Elongated to fit your bowl if you know the your toilet is Round or Elongated.
I hope that helps!
Bemis Manufacturing Company
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