Start with how the space will be used
There is no single number that fits every gathering or worksite. Begin with the expected attendance or crew size, how long the restroom will be needed, and whether permanent restrooms are available. A short daytime gathering has different needs from a multi-day event or an active construction project.
Consider duration, food, and beverages
Longer events create more restroom demand than brief ones. Food and beverage service can also change how often guests use restrooms, so include the menu, alcohol service, and event schedule when planning. For construction, consider the size of the crew on the busiest shift and the length of the project.
Plan for access and accessibility
Units need a level, reachable placement with enough access for delivery and servicing. Include accessible portable toilets when guests or workers need a wider entry, more interior room, or easier approach. Handwashing stations are also an important part of a complete setup.
Ask before you reserve
Share the location, dates, attendance or crew size, existing restroom access, and any special needs with the rental team. A conversation about the actual site is more useful than relying on a generic formula.