A. Rear clearance
Measure from the centerline of the two seat-mounting holes straight back to the first obstruction: the front of the tank, a porcelain rise, or a French curve. Broad retailer guides commonly cite 1.5 inches for some products and 1.75 inches for many electronic seats, but exact models vary.
B. Mounting-bolt spacing
Measure center to center, not outside edge to outside edge. Broad fit guides show approximately 5–7.5 inches for some attachments and 5.5–7.5 inches for many electronic seats. Some specific products are much narrower; TUSHY, for example, publishes a 5.5-inch maximum for the electric models in its cited support article.
C. Bowl length
Measure from the mounting-hole centerline to the outside front edge of the porcelain. One broad guide describes many round bowls as 16.5–17.5 inches and elongated bowls as greater than 18 inches. A current TUSHY support article uses 18.5 inches as its own round-versus-elongated dividing rule. That disagreement is useful: the exact product rule is more important than a universal label.
| Measurement | What it screens | Common mistake |
|---|---|---|
| Rear clearance | Housing collision with tank or curve | Starting at the back edge rather than bolt centerline |
| Bolt spacing | Mounting-plate or bracket range | Measuring outside-to-outside |
| Bowl length | Round, elongated, compact, and overhang risk | Measuring the removable seat instead of porcelain |
Take two photos
- A side view showing whether porcelain rises behind the bolt holes.
- A plumbing view showing the wall shutoff, supply hose, and tank connection—or proving that those connections are concealed.
Photos do not replace measurements, but they help a merchant or manufacturer support team see French-curve and skirted-toilet problems that numbers alone miss.