How many toilets are needed for 45 employees on a construction site?

The minimum would almost always be 3. Under some guidelines, 4 would be required.

This is mandated specifically by OSHA and by regulations in each state or locality. It can vary based on the ratio of male to female workers. The minimum number is almost always 2, which also provides for malfunction in one.

OSHA guidelines are one toilet for each 20 workers on construction sites (one toilet and one urinal for every 40 workers), so for 45 workers, the number would either be 3 or 4.