In general, empty hot tubs can weigh anywhere from 400 to 700 pounds. A 700-pound hot tub is usually designed to hold about 600 gallons. When full, a hot tub of this size weighs about 6,000 pounds and has space for six average-sized adults.
Some hot tubs that fall outside of this weight range. For example, the Swim Spa designed by Spa Manufacturers, Inc., weighs about 2,400 pounds and can hold up to 1,200 gallons of water. Spa Manufacturers also sells a smaller 5-foot by 7-foot spa-style hot tub that weighs 300 pounds when empty and can be filled with 150 gallons of water.