Water Heater Size Calculator
Tank size and first-hour rating target by household size.
You need
50 gallons
Compare models by first-hour rating, not just tank volume.
- First-hour rating target
- 36 gallons
Estimates only. Verify quantities before ordering.
How this is calculated
Tank size: 40 gal for 1 to 2 people, 50 gal for 3 to 4, 65 gal or more for 5 plus, with about 10 gallons added for electric models. First-hour rating target: roughly 12 gallons per person in the busiest hour, plus about 20 gallons if laundry or dishwasher runs during it.
Enter your household size and fuel type, and this calculator recommends a storage tank size plus the first-hour rating (FHR) to look for on the yellow EnergyGuide label. FHR, how many gallons of hot water the unit delivers in a busy hour, is the number that actually matters; tank volume is just the everyday shorthand for it.
Electric models are sized about 10 gallons larger than gas for the same household because electric elements reheat water more slowly than a burner. If your busy hour stacks multiple showers with laundry and the dishwasher, buy toward the high end or shift chores off the peak; an undersized tank shows up as the third shower running cold.
Water heater sizes by household
Rows assume no laundry or dishwasher in the peak hour; add about 20 gallons of FHR if there is.
| Household | Tank size | FHR target |
|---|---|---|
| 1-2 people, gas | 40 gallons | 24 gallons |
| 3 people, gas | 50 gallons | 36 gallons |
| 4 people, gas | 50 gallons | 48 gallons |
| 4 people, electric | 60 gallons | 48 gallons |
| 6 people, electric | 75 gallons | 72 gallons |
Common questions
What size water heater for a family of 4?
A 50 gallon gas or 55 to 60 gallon electric tank is the standard recommendation for 3 to 4 people. More useful: look for a first-hour rating around 65 to 70 gallons if your mornings stack two showers with a laundry load.
What is a first-hour rating?
FHR is how much hot water the heater can deliver in one busy hour, combining the stored volume with how fast the unit reheats. It is printed on the EnergyGuide label. Two 50 gallon tanks can differ by 20 gallons of FHR, which is why it beats tank size for comparisons.
Should I get a tankless water heater instead?
Tankless units are sized completely differently: by flow rate (gallons per minute) and the temperature rise from your groundwater, not by tank gallons. They never run out of hot water but limit how many fixtures run at once. This calculator covers storage tanks; for tankless, add up the GPM of fixtures that run simultaneously.
How long should a water heater last?
Storage tanks typically last 8 to 12 years; tankless units 15 to 20 with maintenance. If your tank is past 10 years and you are seeing rusty water or moisture at the base, size the replacement before it fails, since emergency replacements rarely leave time to compare models.