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Storage Water-Heater Tank Size for a Household Calculator

First-hour rating ≈ 12 gal/person + 5 gal/load (machine).

Estimate the storage water-heater tank size your home needs based on its first-hour rating: 12 gallons per occupant, +14 gal for a hot shower, +20 gal for a clothes washer, +14 gal for a dishwasher running during peak hour. Round up to the nearest standard tank size: 30, 40, 50, 65, 80.

Nadia Almasri By Nadia Almasri
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

FHR ≈ 12·N + 14·showers + 20·washer + 14·dw.

In depth

Estimate the storage water-heater tank size your home needs based on its first-hour rating: 12 gallons per occupant, +14 gal for a hot shower, +20 gal for a clothes washer, +14 gal for a dishwasher running during peak hour. Round up to the nearest standard tank size: 30, 40, 50, 65, 80.