Water Heater Tank Size Calculator

A storage water heater is sized for the busiest hour of the day, not the day itself: can the tank plus its recovery keep a family of showers running without the second person waiting on cold water?

Water Heater Tank Size Calculator estimates peak-hour demand from your household and recommends a standard tank capacity using the first-hour-rating method.

• Peak-hour demand: occupants x gallons per peak hour.
• First-hour rating: match against standard tanks.
• Temperature corrected: scales for your rise.
• Standard sizes: 30 to 80 gallon steps.
• Bathroom aware: extra baths push the number up.
• Export: Copy or download the report.

1. Enter your household size and number of bathrooms.
2. Rate your usage - light, typical or heavy.
3. Set the tank and incoming temperatures.
4. Read the recommended tank size and its first-hour rating.

Example - Family of four, typical usage. 4 people x 20 gal = 80 gal peak-hour demand. A 66 gal gas tank with an FHR near 110 covers it comfortably; a 40 gal electric with a modest FHR may not survive the morning rush.

• No more guess-and-buy: a defensible tank number.
• Gas or electric: same demand math, different FHR.
• Family-aware: adjust for real bathing habits.
• Free and private: no uploads, no logging.