How to use the required plumbing fixtures calculator
Fixture counts drive restroom sizing and therefore core layout, so they are worth checking early. Enter the occupancy classification and the male and female occupant loads, and this tool returns water closets, urinals, lavatories, drinking fountains and the service sink in one pass. Occupant load normally comes from the building code occupant load factors applied to the floor area.
The ratios follow Table 403.1 of the International Plumbing Code. Business occupancies use one water closet per 25 for the first 50 occupants and one per 50 beyond that, with lavatories at one per 40 for the first 80 and one per 80 after. Assembly theaters are counted separately by sex at one per 125 for men and one per 65 for women. Urinals may be substituted for up to 67 percent of the required male water closets in assembly and educational occupancies and up to 50 percent elsewhere, and that maximum is shown alongside the result.
Check which code your jurisdiction has adopted before relying on any number. Large parts of the West Coast use the Uniform Plumbing Code instead, whose tables differ, and many states and cities amend the adopted table or add their own potty parity provisions for assembly uses. Accessible compartments under the ADA and ICC A117.1 are additional requirements, not part of these totals, so confirm the final schedule with your architect or plumbing engineer.
Frequently asked questions
Accessible compartments are counted within the required fixture totals, but their number, size and clearances come from the ADA Standards and ICC A117.1 rather than from the fixture table, so they must be checked separately.
Use the occupant load factors in Chapter 10 of the International Building Code, such as 150 gross square feet per person for business areas, then split it between sexes at 50/50 unless the use clearly differs.