Water Heater Size Calculator
Determine the right water heater tank size or tankless GPM based on household size, usage patterns, and water temperatures.
Inputs
Results
Tank Size
75 gal
≈ 15 buckets
How to Use This Calculator
- Enter Household Size (number of people).
- Select Peak Demand level (Low, Medium, or High simultaneous use).
- Enter Incoming Water Temp (degrees F) and Desired Hot Water Temp (degrees F).
- Input your Electricity Cost ($/kWh) or gas rate.
- Review Recommended Tank size (gallons) and the First Hour Rating needed.
How the result changes with Household Size
| Household Size | Tank Size |
|---|---|
| 1.9 | 40 gal |
| 4.15 | 75 gal |
| 6.85 | 80 gal |
| 9.1 | 80 gal |
What each input means
- Household Size
- Number of people in the household.
- Peak Hour Usage
- How heavily hot water is used during the busiest hour.
- Incoming Water Temp
- Temperature of the cold water supply (varies by region and season).
- Desired Hot Water Temp
- Target hot water temperature at the tap.
- Electricity Cost
- Local electricity rate in dollars per kilowatt-hour.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersHousehold Size = 4, Peak Hour Usage = 2, Incoming Water Temp = 50, Desired Hot Water Temp = 120 = 5 input(s) provided
- Calculate Tank SizeTank Size75 = 75
- Calculate Peak Hour DemandPeak Hour Demand48 = 48
- Calculate Tankless GPM NeededTankless GPM Needed6 = 6
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.
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