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)
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.