Sizing restrooms to the plumbing code
Every commercial building must provide a minimum number of plumbing fixtures based on how many people occupy it and what the building is used for. The International Plumbing Code sets these minimums in Table 403.1 as a ratio — one fixture for every so many occupants — that varies by occupancy group. Too few fixtures fails plan check; too many wastes money and floor area. This calculator takes the occupant load and occupancy type and returns the required count of water closets, urinals, lavatories, and service sinks.
How it works
The occupant load is first split by gender, defaulting to a 50/50 share as the IPC assumes. For each gender the tool applies the per-occupancy ratio from Table 403.1. Some occupancies use a tiered ratio — business use, for instance, is one water closet per 25 persons for the first 50 occupants and one per 50 above that — and the calculator evaluates each tier additively, rounding up within each band.
For men’s facilities, IPC Section 419.2 permits urinals to substitute for up to 67% of the required water closets. When that option is on, the tool moves the allowed fraction of male water closets into the urinal column while keeping at least one water closet. Lavatories follow their own ratio in the same table, and a service sink is required for nearly every occupancy.
Example and notes
A 150-person office at a 50% male split yields 75 men and 75 women. The
business ratio gives 2 men’s water closets (1 for the first 50, 1 more for the
next 25) and 2 women’s, plus lavatories at the office ratio. Enabling urinal
substitution converts one men’s water closet to a urinal. Always verify the
adopted code edition with your authority having jurisdiction — local amendments
frequently change these ratios, and accessible fixtures and drinking fountains
are counted separately.