Water Heater Size Calculator
Calculate the right water heater tank size for your household.
Enter the number of people and usage habits to get a recommendation in gallons or liters.
Recommended Tank Size
Water heater sizing is based on peak hour demand — the most hot water your household uses in a single hour.
Peak Hour Demand = Sum of all hot water activities during the busiest hour
Unit conversions:
Imperial: GallonsMetric: Liters (1 gallon = 3.785 liters)
Hot water usage per activity:
| Activity | Gallons | Liters |
|---|---|---|
| Shower (per person) | 10–15 | 38–57 |
| Bath | 20 | 76 |
| Dishwasher load | 6 | 23 |
| Clothes washer (hot) | 7 | 26 |
| Hand washing | 2 | 8 |
Sizing guidelines by household:
| People | Low Use | Average Use | High Use |
|---|---|---|---|
| 1–2 | 30 gal (114 L) | 40 gal (151 L) | 50 gal (189 L) |
| 3–4 | 40 gal (151 L) | 50 gal (189 L) | 65 gal (246 L) |
| 5+ | 50 gal (189 L) | 65 gal (246 L) | 80 gal (303 L) |
Tips:
- Tankless water heaters are sized by flow rate (GPM), not tank size
- First Hour Rating (FHR) matters more than tank size — check the label
- Gas water heaters recover faster than electric (about 2× the recovery rate)