The survey will take place throughout the city from 8 p.m. to midnight, taking a census of not only people living in the streets but also in homeless shelters and other city-sponsored homeless programs.
Officials say the count helps the city evaluate its current programs and refine its plans to further curtail homelessness.
The count is conducted every two years and is required in order to receive federal assistance, city officials said.
San Francisco's last homeless count, conducted in January 2007, tallied 6,377 people.
