Water Heater Size Calculator
Enter household size and bathroom count — get the recommended tank size in gallons.
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Reference table: gallons by household size
| Occupants | Baseline tank size |
|---|---|
| 1 | 30 gal |
| 2-3 | 40 gal |
| 4 | 50 gal |
| 5 | 60 gal |
| 6+ | 80 gal |
Add 10 gallons to the baseline for 3+ bathroom households — see the worked example below for how that bonus does and doesn't apply. If you're also weighing a tankless unit instead of a tank, see tank vs tankless water heater for how the sizing logic changes completely.
How to use this calculator
Enter the number of people in the household and how many bathrooms the house has. Tank sizing is conventionally based on occupant count — more people means more simultaneous hot water draws (showers, dishwasher, laundry) that the tank's first-hour recovery needs to cover.
Why bathroom count adds to the recommendation
Occupant count drives baseline demand, but a household with 3+ bathrooms has more potential for simultaneous draws (two showers running at once, for example) than the same number of people in a 1-bathroom home — this calculator adds a modest capacity bump for 3+ bathroom households to account for that.
Worked example
A household of 4 with 2 bathrooms: the standard occupant-based table recommends 50 gallons — no bathroom bonus applies since it's under the 3-bathroom threshold.
Frequently asked questions
Does this apply to tankless water heaters?
Not directly — tankless units are sized by flow rate (GPM) and temperature rise needed, not tank gallons. The occupant/bathroom count here is still a useful starting point for how much simultaneous demand a tankless unit needs to handle, but the sizing math is different.
What's "first hour rating" and why does it matter more than tank size alone?
First hour rating (FHR) is how much hot water a heater can actually deliver in the first hour of heavy use — it depends on tank size, burner/element power, and recovery rate together, not tank gallons alone. Two 50-gallon tanks with different recovery rates can have meaningfully different real-world FHR.
Should I round up if I'm close to the next size?
Generally yes, especially if the household's hot water usage runs on the heavier side (long showers, frequent laundry) — a slightly larger tank costs modestly more upfront but avoids running out of hot water during peak demand.
Rule-of-thumb estimate based on commonly published sizing guidance. Reference only — consult a licensed plumber for a precise recommendation, especially for tankless systems.