As of 2015, gas water heaters are available in sizes ranging from 30 to 70 gallons, but 40- and 50-gallon devices are the minimum standard capacities recommended for most homes. The size needed primarily depends on the number of people living in the home.
A 40-gallon tank is considered the minimum capacity for two to four people, and a 50-gallon tank is the minimum needed to support five or more people. A home's fixtures also need to be considered when choosing a new water heater. Deep-soaking tubs hold more water than regular tubs, and older showerheads use more water than newer fixtures, increasing the total household demand for hot water.