Water heater sizing calculator
Tool-first calculator
Water heater sizing: tank gallons or tankless GPM.
Pick a household profile to estimate the right tank capacity or tankless flow rate. Real sizing depends on incoming water temperature, fixture count, and simultaneous use, but this gets you in the right ballpark before a plumber quotes a replacement.
Recommended size
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Local installed cost
What an installer charges for your scope.
The numbers above are material counts and sizing. Below shows what a contractor typically charges in your city for an installed version of this scope, scaled from FatBook's cost index of BLS wages + Craftsman labor hours + permits + materials.
Pick the cost-index service that matches the scope you're scaling. The default is the trade's headline service.
National Average · Water Heater Installation
$1,831
Range $1,613 to $2,066 · lowest realistic price $1,613
How to use this result
- Tank size in gallons is one number to match. First-hour rating (FHR) is the more honest one. Confirm both on the model spec sheet.
- Tankless GPM is the peak flow. Cold climates require a higher GPM unit than warm climates for the same household.
- Electric tank water heaters with the same gallon rating recover slower than gas. If two showers run back-to-back, size up one tier.
Cost-index version: 2026-07-10. Read the FatBook methodology, or use the bid and true cost calculators for a water heater install bid check.