Minimum Plumbing Fixtures by Occupancy (IBC Table 2902.1)
The minimum water closets, lavatories, drinking fountains, and service sink a building must provide from its occupant load and occupancy class: fixtures = ceil(occupants-per-sex / ratio), each rounded up, load split evenly between the sexes. A 100-occupant office needs four water closets (the 1:25 first-tier ratio and the round-up push it past the naive per-50 read), where a 160-occupant restaurant on the 1:75 ratio needs far fewer. The occupancy class, not the head count alone, sets the fixtures. A design aid, not a code-official determination.
Formula and source
per_sex = ol x distribution; wc(sex) = ceil(min(per_sex, wc_tier) / wc_ratio) + (wc_ratio_over > 0 ? ceil(max(per_sex - wc_tier, 0) / wc_ratio_over) : 0); lav(sex) = ceil(per_sex / lav_ratio); fountains = ceil(ol / fountain_ratio); service = 1.
IBC 2021 §2902 and Table 2902.1 (minimum plumbing fixtures by occupancy, mirrored in IPC Table 403.1) and §2902.1.1 (round each ratio up), by name.
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