Service
How Many Do You Need?
On a construction site OSHA requires one facility for 20 or fewer workers, one toilet seat and one urinal per 40 workers at 20 or more, and per 50 workers at 200 or more. Events have no federal ratio, so plan on one unit per 50 guests per four hours.
Construction sites: the federal table
| Number of employees | Minimum number of facilities |
|---|---|
| 20 or fewer | One |
| 20 or more | One toilet seat and one urinal per 40 workers |
| 200 or more | One toilet seat and one urinal per 50 workers |
29 CFR 1926.51(c)(2) adds that under temporary field conditions, provisions shall be made to assure not less than one toilet facility is available.
Fixed workplaces: Table J-1
A fixed workplace runs on a different table, at 29 CFR 1910.141(c)(1)(i), which counts fixtures against total employees rather than crew size.
| Number of employees | Minimum number of water closets |
|---|---|
| 1 to 15 | 1 |
| 16 to 35 | 2 |
| 36 to 55 | 3 |
| 56 to 80 | 4 |
| 81 to 110 | 5 |
| 111 to 150 | 6 |
| Over 150 | One additional fixture for each additional 40 employees |
Events: an estimate, not a rule
OSHA regulates workers, not guests, so there is no federal ratio for events. The planning basis used here is one unit per 50 guests for each four hours, plus about 20 percent when alcohol is served. That is a rule of thumb the operator confirms against your venue, not a regulation.
The calculator on the home page applies both: the federal table for worksites and the planning basis for events, and tells you which one it used.
Accessibility, either way
Where units are clustered, the 2010 ADA Standards section 213.2 Exception 4 caps the accessibility requirement at 5 percent of that cluster, which in practice means at least one accessible unit.
Sources: 29 CFR 1926.51(c)(1) and (c)(2), OSHA. 2010 ADA Standards for Accessible Design, sections 213.2 and 304.3.1, US Department of Justice.
Frequently asked questions
How many porta potties per person?
On a worksite it is set by the OSHA table: one facility for 20 or fewer workers, then one toilet seat and one urinal per 40 workers. For events a common planning basis is one unit per 50 guests for each four hours.
How many porta potties for 100 guests?
On the planning basis above, roughly two units for a four hour event and four for an eight hour event, plus about 20 percent if alcohol is served. Confirm the final count with the operator against your venue.
Does OSHA cover events?
No. OSHA regulates workers, so the federal tables apply to your crew rather than your guests. An event count is a planning estimate.
What if my crew grows mid-project?
The obligation grows with it. The table steps at 20 workers, so a site running 18 needs one facility and the same site at 22 needs one toilet seat and one urinal per 40 workers.
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