What Size Water Heater Do I Need? (2026 Guide)
Count bedrooms, bathrooms and fixtures, then match them to a tank size — see the sizing chart for 1 to 5+ people, gas vs. electric, and the First-Hour Rating rule.
Size to the peak hour, not the average day
Water heater sizing is really about peak demand — the gallons of hot water used in the busiest hour, usually the morning. Two common rules of thumb get you close: count the people, or count the bedrooms and bathrooms. Both are approximate.
The final word is the First-Hour Rating (FHR) on the yellow Energy Guide label — the gallons a full tank can deliver in its first hour of heavy use. Match that rating, not the box size.
Method 1: size by number of people
The fastest estimate starts with the head count — more people sharing the same morning means more stored hot water:
| People in home | Tank size | Notes |
|---|---|---|
| 1-2 | 30-40 gal | 30-gal gas suits light use; pick 40 if electric. |
| 2-3 | 40 gal | The most common choice; covers most schedules. |
| 3-4 | 40-50 gal | Gas stays at 40; electric recovers slowly — lean to 50. |
| 5+ | 50-80 gal | Back-to-back showers plus laundry need the big end; plan 65-80 gal if electric. |
Approximate. Because gas reheats about twice as fast as electric, a gas tank can run 10-20 gal smaller for the same household.
Method 2: size by bedrooms and bathrooms
A second estimate reads the floor plan — more bedrooms and baths mean more people and fixtures sharing one hour. This chart estimates the peak-hour demand you need to cover, in gallons of First-Hour Rating:
| Bedrooms & baths | Peak-hour demand (FHR) |
|---|---|
| 1-2 bed, 1 bath | ~25-35 gal FHR |
| 2-3 bed, 2 bath | ~40-50 gal FHR |
| 3-4 bed, 2-3 bath | ~50-65 gal FHR |
| 4+ bed, 3+ bath | ~65-80+ gal FHR |
Estimates only — demand follows simultaneous use. Two showers plus a dishwasher lands near the top of your range; staggered showers land near the bottom.
Your number in four quick steps
- Count residents — full-time occupants, plus one for frequent guests.
- Count what can run at once — fixtures sharing the peak hour: shower ~10 gal, bathtub 20-30 gal, clothes washer 20-30 gal, dishwasher 6-10 gal per use (industry approximations).
- Add the peak-hour gallons — two showers plus a dishwasher load is roughly 26-30 gal.
- Match it to an FHR — pick a tank whose First-Hour Rating covers that total; the rating, not the box, is the real size.
Prefer not to do the arithmetic? The water heater size calculator turns your household count and fixture list into a tank size in seconds.
Buy to the First-Hour Rating
Every figure above is an estimate. Before you order, read the First-Hour Rating (FHR) on the Energy Guide label or nameplate and confirm it covers your peak-hour total. Between two sizes? Move up one tank — it costs little more to run.
While you're sizing home systems, see our guides on air conditioner sizing and ceiling fan sizing.
FAQ
Do gas and electric tanks need different sizes?
Usually yes — gas reheats in roughly half the time, so the same household can run about 10-20 gal smaller: a family of four is fine with a 40-gal gas tank, but may drain a 40-gal electric one during back-to-back showers. Step electric up to 50. The First-Hour Rating on the label decides.
Do I size a tankless water heater the same way?
No — tankless units hold no water, so size by flow rate (GPM), not gallons. Add the fixtures you might run at once — two showers plus a kitchen sink is roughly 5-7 GPM — and pick a unit rated for that flow at your incoming water temperature.
My family of four: 40 or 50 gallons?
If it's electric — or two showers collide with a dishwasher or laundry — start at 50. With gas, 40 gal handles most four-person homes; move to 50 when showers overlap or you fill a large tub. Verify with the First-Hour Rating.
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