Bidet seat fit: 18.5 inches from the mounting holes to the bowl front is elongated, 16.5 inches is round

Last updated: 2026-10-27

TOTO: measure from the seat mounting holes to the front of the bowl. 18.5 inches is elongated; 16.5 inches is round-front. Buy the matching seat shape.

Brondell: all its bidets need a standard ⅞" fill valve connection.

Sources: TOTO, Will a WASHLET fit a non-TOTO toilet?, Brondell FAQ.

TOTO fit measurements

Check	TOTO's figure
Bowl shape	Elongated: 18.5 in from mounting holes to bowl front. Round-front: 16.5 in.
Space from tank front to mounting-hole center, elongated	At least 2 in
Same, round-front	At least 2-1/2 in for WASHLET C5 or C2; at least 1-3/4 in for S550e and S500e
Distance between mounting holes	About 5-1/2 in, center to center
Flat surface from toilet center to bowl edge	At least 8 in

Source: TOTO fit page. TOTO adds that a French-curve toilet "may prevent WASHLET installation."

Brondell fit notes

"All of our bidets will require access to a Standard ⅞” fill valve."
"If your toilet has a Skirted, One-piece, or French Curve design, additional installation parts may be required."
"Our bidet products are designed to be installed on a standard two piece toilet."

Source: Brondell Flush Installation and Compatibility FAQ.

Sources

TOTO, Will a WASHLET fit a non-TOTO toilet?: https://www.totousa.com/tips/will-a-washlet-fit-a-non-toto-toilet (read 2026-10-27)
Brondell Help Center, Flush Installation and Compatibility FAQ: https://help.brondell.com/hc/en-us/articles/34581171373453-Flush-Installation-Compatibility-FAQ (read 2026-10-27)

Last checked 2026-10-27.