Two different planning problems
A private event needs a practical capacity plan. A construction project also has workplace requirements. Neither should be reduced to a universal guest-to-toilet ratio.
Small private gatherings
For an initial discussion, this tool uses one unit per 50 people for private gatherings of up to 250 guests and four hours without alcohol. It does not subtract indoor bathrooms or claim a legal minimum. Longer events, public events and alcohol service need a custom recommendation.
California construction baseline
The tool rounds each employee category up in groups of 20 under §1526. For fewer than five total employees, it shows the single-user all-gender exception. It does not substitute urinals or subtract existing facilities. Have your safety professional review all exceptions and the actual layout.
Example: 21 male workers and 3 female workers give 2 + 1 = 3 toilet facilities. For handwashing, 24 workers divided into groups of 20 gives 2 washing stations under §1527. Confirm that the selected washing equipment meets the rule.
For nonwater carriage toilets, §1527 generally places the washing facility outside and unattached to the toilet. It includes an exception for fewer than five employees with one toilet.