Tank Volume Calculator
Tank capacity in gallons.
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Home & Garden
Water Heater Size Calculator
Get a recommended tank size and tankless flow from household size.
Tank size
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Recommended.
| Tankless flow | — |
|---|---|
| First-hour rating | — |
| People | — |
| — |
Show our math
Enter your figures above to see the step-by-step working.
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How the Water Heater Size Calculator Works
A storage water heater is sized by its first-hour rating — how much hot water it can deliver during a busy hour — which scales with household size. As a guide, 1–2 people suit a 40-gallon tank, 3–4 people a 50–60-gallon tank, and 5 or more a 66–80-gallon tank. A tankless heater is sized instead by flow rate in gallons per minute, driven by how many fixtures might run at once.
Enter your household size and number of bathrooms for a recommended tank size and the rough tankless flow rate you’d need.
tank size scales with people; tankless flow scales with simultaneous fixtures
Frequently Asked Questions
What size water heater do I need?
Roughly 40 gallons for 1–2 people, 50–60 for 3–4, and 66–80 for 5 or more — based on peak-hour hot-water demand.
Tank or tankless?
Tank heaters store a set amount; tankless heat on demand and are sized by flow rate (GPM). Tankless never runs out but must be sized for simultaneous use.
What is first-hour rating?
The gallons of hot water a tank can supply in an hour starting full — the key number for matching a tank to your household.
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