Short answer
40 and 50 gallons are the common home sizes. Fixr pairs a 40 gallon tank with 1 to 4 people and a 50 gallon with 3 to 5, but the reliable test is the first hour rating: it should at least match the hot water used in your busiest hour (20 gallons per shower in the DOE worksheet). Before you buy, measure the height, width and door clearance: a tall and a short version of the same capacity can differ by about 10 inches in height.
Gallons vs first hour rating
Gallons are the tank volume. The first hour rating (FHR) is how much hot water the heater can deliver in one hour starting full, and it depends on tank size, fuel and the size of the burner or element (DOE). Two 50 gallon tanks can have quite different first hour ratings, which is why the DOE says to size by FHR. Get your target from the tank size calculator.
Common sizes and who they suit
Tank sizes by household
| Size | Household (Fixr) | Installed cost (Fixr 2026) | Typical use |
|---|---|---|---|
| 30 gallon | 1 to 2 people | $550 to $2,100 | Apartments, condos, one bathroom |
| 40 gallon | 1 to 4 people | $550 to $2,300 | One or two bathrooms, gas tanks especially |
| 50 gallon | 3 to 5 people | $700 to $2,500 | Family homes, electric tanks especially |
| 75 gallon | 4 to 6 people | $1,100 to $3,400 | Several bathrooms, soaking tubs |
| 80 gallon | 6 or more people | $1,200 to $3,600 | Large households, mostly electric and heat pump |
Fixr’s household column is a starting point. Use it to shortlist, then confirm with the first hour rating.
Tall vs short tanks
Most capacities come in a tall version and a short (lowboy) version. Retail spec sheets for 50 gallon electric tanks show the spread: a short model at about 49.25 inches tall and 23 inches across, and tall models at about 55 to 59 inches tall and 20.5 inches across. Your manual or the maker’s spec sheet has the exact numbers for any model.
Measure before you buy
- Height to the ceiling or shelf, leaving room on top for the pipes, the vent connector on gas tanks, and the anode rod if you want to pull it out later.
- Width and depth, including the drain pan. Pans are sold by inside diameter, so a wider tank may need a larger pan.
- Doorways and stairs the tank has to travel through, in its box.
- Clearances the manual asks for around gas tanks and for air around heat pump models.
Small and point of use tanks
Mini tanks of about 2.5 to 7 gallons sit under a sink or on a shelf and feed one fixture. They do not replace a main water heater; they bring hot water fast to a sink far from it. Some plug into a 120 volt outlet; larger ones are hardwired.
Questions people ask
What is the most common water heater size?
40 and 50 gallon tanks are the sizes most homes use. Fixr lists them for households of 1 to 4 and 3 to 5 people. Smaller 30 gallon tanks suit 1 to 2 people; 75 and 80 gallon tanks suit larger households.
Can I replace a 40 gallon water heater with a 50 gallon?
Usually yes, if it fits the space, the drain pan and the doorway, and the vent or circuit suits the larger model. Check the first hour rating too: a 40 gallon gas tank with a strong burner can outdo a 50 gallon electric tank.
How tall is a 50 gallon water heater?
It depends on the model. Retail spec sheets show a short 50 gallon electric tank at about 49 inches tall and 23 inches wide, and tall versions at about 55 to 59 inches tall and about 20.5 inches wide. Measure your space and check the spec sheet.
What is the difference between tall and short water heaters?
They hold about the same water. Short (lowboy) tanks are wider and fit under stairs, in crawl spaces or under counters; tall tanks are narrower and fit closets.
Sources
Last reviewed October 29, 2026. Models, codes and listings change; check your heater’s manual and your local code, and follow the maker’s instructions.