I do not believe that has been determined.A preliminary study about 15 years ago planned on launching an unmanned habitat module, stocked with crew quarters and enough supplies for four persons staying six hundred days. This would also include some sort of descent system to land the habitat module safely on Mars. The descent system is a major unknown as no existing landing system the U.S. has scales up to the habitat module's mass.
Two years after the habitat module safely lands, the crew would be launched from Earth in a similar mass vehicle. The outbound trip would take about six to 10 months depending on orbital mechanics. An unfueled ascent stage would be included as part of the vehicle that will land close to the already operating habitat module. The ascent stage would be fueled on Mars by a manufacturing plant included in the habitat module.
My estimate would be three to four SLS vehicles. Six to eight months for the outbound journey, two years on Mars, and six to eight months return.