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Minimum Plumbing Fixtures by Occupancy (IBC Table 2902.1.1)
The minimum water closets, lavatories, drinking fountains.
Example
You enter
- Occupant load (persons) 100
- WC ratio, first tier (occ/WC) 25
- WC ratio above tier (0 = n/a) 50
- First-tier size per sex (0 = single) 50
- Lavatory ratio, first tier (occ/lav) 40
- Fountain ratio (occ/DF) 100
- Share as one sex (0-1) 0.5
You get
- Water closets (total) 4
- Lavatories (total) 4
- Drinking fountains 1
- Service sinks 1
Checked against published worked examples from: Gustin Design Services; Dalkita.
Details, formula, and sources
ScopeThe 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 the same four for 60% more people. The occupancy class, not the head count alone, sets the fixtures. A design aid, not a code-official determination.
Formula or tableper_sex = ol x distribution; wc(sex) = (wc_tier > 0 and wc_ratio_over > 0) ? ceil(min(per_sex, wc_tier) / wc_ratio) + ceil(max(per_sex - wc_tier, 0) / wc_ratio_over) : ceil(per_sex / wc_ratio); lav(sex) the same form with lav_tier / lav_ratio / lav_ratio_over; fountains = ceil(ol / fountain_ratio); service = 1.
Source and editionIBC 2027 §2902 and Table 2902.1.1 [Table 2902.1 in IBC 2021] (minimum plumbing fixtures by occupancy, mirrored in IPC 2027 Table 403.1.1 [403.1 in IPC 2021]) and §2902.1.1 (divide the load in half by sex, round each ratio up), by name.
Free accessThe fixture-count relation is stated in the published IBC §2902 / Table 2902.1.1 (2902.1 in 2021); the arithmetic is public. The ratios are the table values for the occupancy.
What governsEstimate. AHJ and licensed professional govern.
API field namesoccupant_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 2027 §2902.1.1 (also 2021)
- Round up each fixture ratio rounds up per §2902.1.1, so the 1:25 first tier undercounts on a naive per-50 readIBC 2027 §2902.1.1
- Ratio source the bundled ratios are representative; the occupancy class and the AHJ-adopted edition set the governing ratiosIBC 2027 Table 2902.1.1 [2902.1 in IBC 2021]