Calculator
Water heater size calculator
Use your busiest hour. A morning rush might include showers, face washing, laundry, and a dishwasher cycle.
Compare this estimate with the model's first hour rating, not only the storage capacity printed on the tank.
Quick answer
Most homes land somewhere in the 40 to 80 gallon range, but the right tank size depends on household habits. A smaller home can need more capacity if several people shower back-to-back, while a larger household may be fine with less if hot water use is spread throughout the day.
If you are asking how many gallons your water heater should be, the practical question is: how much hot water do you use during your busiest hour?
How to calculate peak-hour demand
American Water Heaters recommends starting with household hot water usage. Their sizing guidance notes that a typical shower uses about 2 to 2.5 gallons per minute, a dishwasher uses about 6 gallons per cycle, and a washing machine may use about 15 to 30 gallons per load.
Add the hot water activities that happen in the same busy hour, then compare the total with the heater's first hour rating. First hour rating matters because it reflects stored hot water plus recovery during use.
Tank size rules of thumb
- 1 to 2 people: often around 30 to 40 gallons.
- 3 to 4 people: often around 40 to 50 gallons.
- 5 or more people: often around 50 to 80+ gallons, depending on usage.
What about tankless?
Tankless water heaters are sized by flow rate, not tank gallons. For tankless, add the gallons per minute of fixtures that may run at the same time, then account for temperature rise. Two showers and a sink can require a much different tankless unit than one shower at a time.
If you are comparing tank, tankless, and heat pump water heaters, use the lifetime ownership cost calculator after you estimate demand.
When to ask a plumber
Use this as a planning estimate before getting quotes. A licensed plumber should confirm fuel type, venting, electrical or gas capacity, space, code requirements, and whether your home needs upgrades such as an expansion tank or drain pan.