Code counts fixtures from the space's occupant load, split half male and half female, using a ratio table by use. An office needs one toilet per 25 people for the first 50 of each sex, a restaurant one per 75, retail one per 500. Phoenix uses one table for both plumbing codes.
What are the ratios for a restaurant, an office and a retail store?
These are the model code numbers from the plumbing fixture table (IPC Table 403.1, which mirrors IBC Table 2902.1). Water closets and lavatories are counted per sex. Drinking fountains and service sinks are counted on the total occupant load.
| Use | Water closets (each sex) | Lavatories (each sex) | Drinking fountains | Service sink |
|---|---|---|---|---|
| Restaurant (A-2) | 1 per 75 | 1 per 200 | 1 per 500 | 1 |
| Office or other business (B) | 1 per 25 for the first 50, then 1 per 50 | 1 per 40 for the first 80, then 1 per 80 | 1 per 100 | 1 |
| Retail store (M) | 1 per 500 | 1 per 750 | 1 per 1,000 | 1 |
Phoenix uses this one table no matter which plumbing code the designer picks. The city's amendment to the Uniform Plumbing Code says to "replace UPC Table 422.1 and footnotes with 2024 International Plumbing (IPC) Table 403.1."
What does that look like for a real space?
Mesa's plan checklist walks through an office. With 538 occupants, that's 269 male and 269 female. Male water closets: the first 50 at 1 per 25 is 2, and the remaining 219 at 1 per 50 is 4.38, so 6.38 rounds up to 7. Female is the same, 7. Lavatories come out at 5 per sex. Drinking fountains: 538 divided by 100 is 5.38, so 6.
Here's a smaller one, an office with 60 occupants (30 and 30). Each sex needs 2 water closets and 1 lavatory. The space also needs one drinking fountain (60 divided by 100, rounded up) and one service sink. A restaurant with an occupant load of 60 needs 1 water closet and 1 lavatory per sex plus a service sink, before the kitchen fixtures are added. It also needs a drinking fountain (one per 500 occupants in that use, and Phoenix waives fountains only at 50 occupants or fewer), unless it provides drinking water in a container free of charge, which is the restaurant exemption covered in our drinking fountain page.
Two rules change the math:
- Urinals can replace water closets, but no more than 50 percent of the male water closets in most uses (67 percent in assembly and educational). Phoenix and Mesa both carry that language.
- Single-user and all-gender rooms count toward the totals. The code's fixture count can be met by separate facilities, single-user rooms or any mix (see single-user and all-gender restrooms in a small tenant space).
### What about a warehouse, a factory or a classroom?
Other commercial uses use the same method with lighter ratios. This extract from the 2024 IBC table, as summarized by DataDrivenAEC, covers common ones. The source notes it is a limited extract, not the full table with its footnotes, so treat it as a starting point and check the full table for your use.
| Use | Water closets | Lavatories | Drinking fountains | Service sink |
|---|---|---|---|---|
| Factory and industrial | 1 per 100 | 1 per 100 | 1 per 400 | 1 |
| Storage (low and moderate hazard) | 1 per 100 | 1 per 100 | 1 per 1,000 | 1 |
| Educational | 1 per 50 | 1 per 50 | 1 per 100 | 1 |
A storage building with 80 occupants (40 male, 40 female) works out to 1 water closet and 1 lavatory per sex, one drinking fountain and one service sink. A mixed-use tenant, such as a retail counter with a back-room warehouse, is counted by the use of each area, and your plan reviewer decides how the occupancies are separated.
### Where does the occupant load come from?
Every number in the table hangs on the occupant load. It is set by the design team, not by how many employees you have on payroll. The building code assigns a load per square foot for each kind of use, or counts fixed seats where there are any, so a dining room carries a much higher load than the same floor area used as an office. The number goes on the plans, usually on the code summary sheet, where the plan reviewer checks it against the use, and the plumbing count follows it. If a tenant expects more people than the plans show, for example a busy lunch crowd, raise it with the architect before permits are filed, since fixing a count after rough-in means opening finished work. That is why the count for a restaurant can be larger than expected for a small footprint, and why changing a space's use can change the fixture count even if no walls move. Our page on what changes when a retail space becomes a restaurant shows how that plays out.
### What mistakes come up most?
- Forgetting to round up. Every fraction rounds up to the next whole fixture, per sex.
- Counting the wrong total. The split is half male and half female unless the design shows otherwise, so the two sides can't share one fixture to save space, except through single-user or all-gender rooms.
- Skipping the service sink. Most uses in the table list one, and Mesa's exceptions for small business and mercantile spaces do not apply everywhere.
- Assuming the last tenant's count carries over. A new use starts a new calculation.
Which small spaces get relief in Phoenix and Mesa?
Cities amend the model code so tiny tenants aren't forced to build two restrooms. In Phoenix, separate men's and women's rooms aren't required for:
- structures or tenant spaces with a total occupant load of 15 or fewer, employees and customers combined,
- mercantile occupancies with 50 or fewer occupants,
- business occupancies with 50 or fewer occupants, and
- single-user rooms, or rooms designed for all persons with privacy for water closets and urinals.
Phoenix also drops the drinking fountain requirement for an occupant load of 50 or fewer. Mesa's version: separate toilets aren't required at 25 or fewer, drinking fountains at 50 or fewer, and service sinks aren't required in business and mercantile spaces up to 100 occupants.
What fixtures does a restaurant need beyond the count?
The occupant-based table covers restrooms and the basics. Kitchens add their own list. Maricopa County's food-establishment plan review requires a hand sink within about 25 feet of food and beverage workstations, a three-compartment sink, a mop or service sink within 300 feet, toilet facilities for employees, and hot or tempered water at every sink. The county says customer restroom counts are deferred to the city, usually using this same IPC table. Grease interceptor sizing is a separate calculation (see what size grease interceptor a restaurant needs).
### Where does accessibility fit in?
On top of the count, assembly and mercantile occupancies with six or more water closets need an accessible family or assisted-use toilet room, per the IBC provision Mesa's checklist cites. Fixture heights and clearances follow the ADA, covered in ADA commercial restroom plumbing.
What's the next step for a tenant?
Warehouses and factories use different ratios, which we cover in adding a restroom to a warehouse or industrial space.
Get the occupant load from your architect or the city's plan review first, since every number above hangs on it. Then run the table for your use, apply the small-space exceptions for your city, and add the kitchen list if you're serving food. If you're mapping a build-out, commercial tenant improvement plumbing shows how the pieces fit together, and HQ gives free estimates on commercial plumbing work.
Once the fixture count is set, the drains behind them are sized by load, as covered in how commercial drain lines are sized with drainage fixture units.