Measure to the glass, not the frame
Section 603.3 sets its limits at the bottom edge of the reflecting surface. That is the edge of the part that actually reflects, not the frame, the channel, or the hanging bracket. A wide bottom frame rail can sit below the limit while the glass above it does not.
Measure up from the finish floor. Over a lavatory or countertop, the limit is 40 in. Any other mirror, including a full-length mirror on an open wall, is limited to 35 in. Both figures are maximums, so glass that starts lower still meets the height rule.
Mirrors, lavatories, and countertops
The accessible lavatory has the front of the higher of its rim or counter surface at 34 in. maximum under 606.3. Its clear floor space is positioned for a forward approach under 606.2, so the user faces the lavatory and the wall behind it. Above that lavatory, 603.3 keeps the glass starting at 40 in. or lower.
In a toilet or bathing room, 213.3.5 requires at least one mirror to meet 603.3 wherever mirrors are provided. The text does not say which one. A mirror away from the lavatories, with its glass starting at 35 in. or lower, is one way to meet it. Advisory 603.3 adds that a single full-length mirror can serve more people, including children.
State and local codes may be stricter here, and the authority having jurisdiction has the last word on which mirror counts.
Mistakes that leave the glass too high
One mistake is setting every mirror by the backsplash or tile line, which can push the glass above 40 in. Another is measuring to the bottom of the frame or the mounting clip instead of the reflecting surface.
A third is treating a side wall or full-length mirror as if the 40 in. limit applied. A mirror that is not over a lavatory or countertop has a 35 in. maximum.
Mirrors with built-in shelves raise a projection question. On a circulation path, 307.2 caps protrusion at 4 in. That cap covers any leading edge higher than 27 in. and no higher than 80 in. off the floor.
Choosing a restroom mirror
On the product drawing, find the distance from the bottom of the frame to the start of the glass. Add that offset to the height of the frame's bottom edge to see where the reflecting surface will begin.
To follow Advisory 603.3, pick a mirror tall enough to put its top edge at 74 in. or higher. The bottom of the glass still has to meet the limit. That 74 in. figure comes from advisory text, so treat it as a recommendation. For shelf or combination units, compare the stated projection with 307.2 before placing one on a circulation path.
