How Many Porta Potties Do I Need?
For an event, start at one unit per 50 guests for four hours and add from there. For a job site the number is federal law rather than guidance: 29 CFR 1926.51(c). Both tables are below, and the calculator uses nothing else.
Event ratios, from ANSI/PSAI Z4.3
| Guests | 4 hours | 6 hours | 8 hours |
|---|---|---|---|
| 50 | 1 | 2 | 2 |
| 100 | 2 | 3 | 3 |
| 250 | 5 | 6 | 7 |
| 500 | 10 | 12 | 13 |
| 1,000 | 20 | 23 | 25 |
| 2,500 | 50 | 56 | 63 |
Add roughly 15–20% where alcohol is served, because people drink more and stay longer. Add one hand-wash station per four units where food is served.
Job sites, from 29 CFR 1926.51(c)(1)
| Workers on site | Minimum required |
|---|---|
| 20 or fewer | 1 toilet |
| More than 20 | 1 toilet seat and 1 urinal per 40 workers |
| More than 200 | 1 toilet seat and 1 urinal per 50 workers |
These are minimums, not targets. A crew that loses ten minutes each way walking to a single unit costs more in time than the second unit costs to rent.
ADA units
Any event open to the public should have at least one wheelchair-accessible unit, and the common industry guidance is 5% of the total with a minimum of one. They are also the first thing to run out on a busy weekend, so book that one before the rest. 1094 of the 1,976 companies we checked say they rent them.
Weddings and private parties
The ratio is the same Z4.3 arithmetic, but two things about weddings change the answer in practice. The event runs long, often seven or eight hours once you count setup and the tail end of the reception, which pushes you up the table faster than people expect. And drinks are served for most of it, which is the 15 to 20 percent adjustment.
The other difference is what you rent rather than how many. A standard unit is fine behind a tent at a working farm and badly out of place at a formal reception, which is why restroom trailers exist and why they are priced the way they are. A two-station trailer covers roughly the same headcount as three or four standard units for a short event, so the count from the calculator above is not the count you order once you switch to a trailer. Ask the supplier what their trailer is rated for and work from that.
How often they need servicing
The number of units and the service interval are the same question asked twice. A unit is rated for roughly 200 to 250 uses between services, so a single toilet at a busy event hits that inside a day, while the same toilet on a five-person job site will go a week comfortably.
Weekly service is the standard interval on long-term rentals and it is what almost every monthly rate assumes. If your site runs more than about ten people to a unit, or the unit is somewhere hot, say so when you book and expect to pay for a second visit each week. Under-servicing is the single most common reason a site with technically enough toilets still has a problem with them.
Where to put them
Three constraints decide placement and they usually conflict. The service truck needs to reach each unit with a hose, which in practice means within about 25 feet of somewhere it can park. Users need them close enough to actually walk to, because a unit nobody uses does not count toward your ratio. And nobody wants them next to the food, the bar or the top table.
On a job site, spread them rather than banking them all at the gate. OSHA sets the count but walking time sets the cost, and a crew crossing a large site twice a day loses more money than the extra unit costs. On an event site, split the total across at least two locations once you are past about six units, and light the route if the event runs after dark.
Hand-wash stations go beside the units, not with the catering, at roughly one per four toilets where food is served. Who rents hand-wash stations.
What people get wrong
Counting heads instead of counting hours. Five hundred people over four hours and five hundred over eight are different jobs, and the table above is the reason.
Counting tickets instead of counting attendance, which is the same mistake wearing a different hat and the one that costs most at a festival. Six real jobs worked through end to end, including that one.
Forgetting staff, crew and vendors. They are on site longer than the guests and they are rarely in the headcount somebody gives the supplier.
Ordering the ADA unit last. It is the scarcest thing in most fleets on a summer weekend, so it is the one to book first rather than the one to add if the budget stretches.