Put in your headcount and who'll use the units. You get the federal minimum for seats and urinals, how many accessible units the ADA asks for, and how often each one should be pumped and cleaned, with the rule behind every number.134
The calculator
Use the most people on site at one time, not a daily average. Pick construction for a jobsite and general industry for a plant, warehouse or yard that isn't a construction project.
Behind each answer
They don't come from one place. Two are federal regulations, one is the ADA design standard and one is an OSHA letter pointing to an industry standard.
29 CFR 1926.51 Table D-1: one facility up to 20 workers, then one seat and one urinal per 40 workers, and per 50 at 200 or more. The rows overlap at exactly 20 and 200, so the calculator takes the higher count there.1
ConstructionTable D-1
29 CFR 1910.141 Table J-1 counts each sex on its own: 1 for up to 15, 2 for 16 to 35, up to 6 for 111 to 150, then one more for each extra 40. Urinals can stand in on the men's side, but water closets can't drop below two thirds of the minimum.2
General industryTable J-1
Where single-user portable units are clustered, no more than 5 percent of each cluster has to be accessible, and a fraction rounds up to the next whole unit. Units used only by construction workers on the site are exempt.3
2010 ADA Standards213.2, 104.2, 203.2
OSHA says an unsanitary toilet doesn't count as provided. Its 2006 letter points to ANSI Z4.3: a toilet used by up to 10 people is serviced at least once a week, and one toilet for 20 workers serviced twice a week would likely be sanitary.4
OSHA letterMay 17, 2006
Worked examples
Table D-1 lets one seat cover up to 40 or 50 people. Run that through the service example in OSHA's letter and the minimum count needs a truck four or five times a week. That's why most crews end up with more units, not more visits.
| Workers | Seats | Urinals | People per seat | Visits a week |
|---|---|---|---|---|
| 8 | 1 | 0 | 8 | 1 |
| 15 | 1 | 0 | 15 | 2 |
| 45 | 2 | 2 | 22.5 | 3 |
| 120 | 3 | 3 | 40 | 4 |
| 260 | 6 | 6 | 43.3 | 5 |
| 400 | 8 | 8 | 50 | 5 |
Seats and urinals from Table D-1. Visits are people per seat divided by 10, rounded up, which is our scaling of the letter's example and not a number in the regulation.14
What crews actually ordered
Over the two years from October 26, 2024 to October 26, 2026, our provider network delivered 26,067 standard construction portable toilets, canceled orders left out. 23,450 of them, about 90 percent, were set up for weekly service.
Put that next to the table above and the pattern is clear. If a unit is only getting one visit a week, the letter's example says it should be shared by about 10 people, so the way to stay there is more units. Where there isn't room for more units, more visits is the other lever.
The same window had 1,971 ADA units go out across the network.
What a headcount can't tell you
OSHA's 2005 letter uses less than 10 minutes to reach a toilet as the general starting point. On a tall building or a long linear job, that can mean splitting the same count across more spots.5
A unit that's full or filthy doesn't count toward Table D-1 at all, per the 2006 letter. Heat, a bigger crew than planned or a long weekend can all push a unit over before its next visit.4
The toilet table doesn't apply to mobile crews with transportation readily available to nearby toilets. A paving or utility crew that moves every day may fall under that.1
The ADA exemption only covers units used by construction workers. A sales office, a festival or a site that lets visitors use the toilets brings the 5 percent rule back.3
Tell us the number from the calculator, how long the job runs and whether the public will use the units. We'll come back with units and a service schedule from the provider network.
Questions
Table D-1 doesn't say. It lists seats and urinals but not how a unit with both is counted. Ask your safety lead before you rely on it.
Not for units used only by construction workers. If anyone else uses them, the 5 percent rule for clusters applies, and some permits and contracts ask for one either way.3
Table J-1 is applied to each sex on its own. Single-person rooms that lock from the inside are the exception, and they don't need to be separated.2
No. The regulation requires sanitary toilets but gives no interval. The calculator scales the example in OSHA's 2006 letter, which uses ANSI Z4.3 as a guide.4
This page does the math. The planning guide covers how to plan above the minimum, with examples from completed orders.
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Sources