Water Heater Size Calculator
Tank or tankless size for your home.
Enter your values
Results update instantly as you type — no submit needed.
Results
- Recommended tank size
- 70 gallons
- Tankless flow needed
- 4.4 gpm
- Required heating capacity
- 154,000 BTU/h
- First hour rating target
- 112 gallons
- Peak demand
- 264 gallons/hour
Quick answer
Tank heaters are sized on first hour rating and household size; tankless units are sized on peak simultaneous flow.
How to use the Water Heater Size Calculator
- 1Enter household size and bathroom count.
- 2Estimate how many fixtures run at once.
- 3Set the temperature rise for your climate.
Frequently asked questions
Tank or tankless?
Tankless suits steady demand and saves standby losses; tanks handle short heavy peaks better.
What is first hour rating?
The gallons a tank can deliver in one hour starting fully hot — the number that really matters.