Ask around a jobsite and you will hear that OSHA requires one portable toilet per ten workers. It is quoted confidently, it appears in vendor literature, and it is not what the regulation says.
What 29 CFR 1926.51 actually requires
Table D-1 sets the construction standard by headcount. Twenty or fewer employees: one facility. Twenty or more: one toilet seat and one urinal per 40 workers. Two hundred or more: one toilet seat and one urinal per 50 workers. There is no 1:10 anywhere in it.
So where does 1:10 come from?
ANSI/PSAI Z4.3, a voluntary standard that sits above the OSHA floor. And it is not a headcount ratio at all — it is a servicing ratio. A unit used by up to ten people is serviced at least once per week. The ratio and the service interval are one sentence, not two competing rules.
How to size a site
Start from peak shift count, not average — OSHA counts the maximum on site at one time, so a crew that doubles for a two-week tie-in sizes the order. Then adjust for the things the tables do not cover: Gulf Coast heat drives usage up, long walks to a single bank cost you more in lost time than a second bank costs to rent, and ADA units are a separate count.
Where the standards stop
The regulation is a floor, not a target. If your site is remote, hot, or running extended shifts, the honest answer is more units or more frequent service than the table requires. That is a conversation with dispatch, not a lookup.
Dispatch answers 24 hours · 7 days · 365. If you are working out how to scope a job, call rather than guess.