UPC Section 408 requires a shower compartment to have at least 1,024 square inches of finished interior floor area and enough room to fit a 30-inch circle. That size must hold up to 70 inches above the drain. Phoenix enforces this figure under the 2024 UPC.
The Uniform Plumbing Code is published and copyrighted by IAPMO. This page explains the section in our own words with a short excerpt only. Read the full official text at the source.
A shower stall that is too small to actually stand and wash in is more than a comfort problem. It fails inspection. UPC Section 408 is the rule that sets the floor. It tells a builder or remodeler exactly how much finished floor space a shower needs and how a plan reviewer checks that space against a fixed shape. Get the number right and the shower passes on the first look.
What this section says
The rule uses two tests together. A shower compartment needs a minimum finished interior area of 1,024 square inches. It must also be shaped so a 30-inch-diameter circle fits inside it. Both tests have to pass. A long, narrow stall can hit 1,024 square inches on paper and still fail if nothing close to a 30-inch circle fits inside it. Here is the core language from the code:
Shower compartments shall have a minimum finished interior of 1,024 square inches (0.66 m2) and shall also be capable of encompassing a 30-inch (762 mm) diameter circle.
In plain terms, that works out to roughly a 32 by 32 inch usable space. A square that size clears both the area figure and the circle test, which is why it shows up so often in finished bathrooms. These are finished interior dimensions, measured inside the tile and wall surround, not the rough framed opening. A remodel that frames a tidy 32-inch square can end up undersized once the tile and backer board eat an inch off each wall.
When this section comes into play
This section governs every new shower and every tub-to-shower conversion in a Phoenix bathroom remodel. For example, a standard alcove tub runs about 60 by 30 inches, so floor space is rarely the obstacle in that swap. The real work is keeping the finished stall at or above 1,024 square inches once the pan, tile, and surround are all in place.
The required area also has to hold up as the walls rise. Section 408 keeps both the 1,024 square inches and the 30-inch circle in place from the finished floor to 70 inches above the drain. A sloped ceiling, a knee wall, or a built-in bench that intrudes into that zone can shrink the legal compartment even when the floor measurement alone looks fine. A corner seat or a recessed niche is fine as long as the circle and the square-inch figure still clear within that 70-inch height. Designers keep those features low or off to the side so the open standing area stays legal. Where the shower sits under a different code, this figure changes. The [International Residential Code](https://codes.iccsafe.org/content/IRC2021P1/chapter-27-plumbing-fixtures), Section P2708, allows a smaller 900-square-inch residential shower with the same 30-inch circle rule. A 30-by-30-inch shower kit built to that number is legal under the IRC but short of the UPC figure Phoenix enforces.
What this means for you
If you are planning a bathroom remodel or a tub-to-shower conversion, size the rough framing larger than 32 by 32 inches so the finished box still clears 1,024 square inches after tile and board go up. Center the drain in the open standing area too, since the 30-inch circle is measured around it, and a drain pushed into a corner can fail the circle test even on a stall with enough floor area. See our page on minimum shower size by code for the full breakdown, including the entry opening width and door swing rules that travel with this one. A remodel that moves or adds a shower usually needs a permit, so check whether a Phoenix bathroom remodel needs a permit.
This figure only applies where the UPC governs. Phoenix does, under the 2024 edition, but Arizona has no single statewide plumbing code, so a nearby town could enforce a different edition or the IRC's smaller number instead. Confirm what plumbing code Phoenix uses for your address before you buy a pan or order glass, especially if the project sits near a city line. The same layout planning covers fixture spacing, so it helps to know the toilet clearance the code requires.
Full text and source
UPC Section 408 is part of the Uniform Plumbing Code. IAPMO publishes and holds the copyright on it. The excerpt above reflects the section as adopted. Phoenix enforces the 2024 UPC with local amendments as part of its Building Construction Code, effective August 1, 2024. Read the current section directly on UpCodes, or confirm local amendments with the City of Phoenix Planning & Development Department: phoenix.gov/pdd.