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.

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.

The fixture-count relation is stated in the published IBC §2902 / Table 2902.1; the arithmetic is public. The ratios are the table values for the occupancy.

Estimate. AHJ and licensed professional govern.

Field names used by the API: occupant_load, wc_ratio, wc_ratio_over, wc_tier, lav_ratio, fountain_ratio, distribution, wc_total, lav_total, fountains, service_sinks

• Per sex the occupant load splits evenly between two sexes (0.5 each) unless a distribution override is suppliedIBC 2021 §2902.2
• Round up each fixture ratio rounds up per §2902.1.1, so the 1:25 first tier undercounts on a naive per-50 readIBC 2021 §2902.1.1
• Ratio source the bundled ratios are representative; the occupancy class and the AHJ-adopted edition set the governing ratiosIBC 2021 Table 2902.1