Water Heater Size Calculator
Estimate the water heater capacity your household needs — tank gallons for a storage heater, or peak flow (GPM) for a tankless unit.
Water Heater Size Calculator
Estimate the tank size (gallons) or tankless flow (GPM) your household needs.
Your recommended water heater size will appear here.
Storage tank
—
recommended capacity
Tankless flow
—
peak demand
Actual sizing also depends on your incoming water temperature and fixture flow rates. This tool provides a rough estimate for general informational purposes only and is not professional advice, a guarantee, or a quote. Results may not reflect your specific situation. Always confirm with a licensed HVAC professional before making any purchase or decision. See our Terms of Service for details.
Frequently Asked Questions
What size water heater do I need?
For a storage tank, plan roughly 10–12 gallons per person; a family of four typically needs a 40–50 gallon tank. Tankless units are sized by peak flow (GPM) instead of gallons.
Is tankless better than a tank water heater?
Tankless heaters deliver endless hot water and save space and standby energy, but cost more upfront and must be sized to peak demand. A tank is cheaper to install but runs out during heavy use.