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How many people regularly use hot water in the home.
Count everyone in the household, not just adults — teenagers and kids taking showers factor into peak demand too.
Recommended tank size
57.5 gallons (recommended)
This is a rough rule-of-thumb range. Homes with multiple bathrooms used simultaneously, soaking tubs, or high-flow fixtures should size toward the higher end or consider a tankless system sized by flow rate instead.
- Recommended range, low
- 50 gal
- Recommended range, high
- 65 gal
They open the calculator with your figures already in it
Water Heater Sizing Calculator: 57.5 gallons (recommended) — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Rule-of-thumb ranges: 1-2 people need 30-40 gallons, 3-4 people 50-65 gallons, 5+ people 65-80 gallons
Inputs used
- Household Size
- 3-4 people
Intermediate steps
- Recommended range, low
- 50 gal
- Recommended range, high
- 65 gal
Confidence note: This is a rough rule-of-thumb range. Homes with multiple bathrooms used simultaneously, soaking tubs, or high-flow fixtures should size toward the higher end or consider a tankless system sized by flow rate instead.
What this calculation does not cover
- Sizes stored volume only — the heat source is not in the model. A gas, electric-resistance and heat-pump tank of the same nominal size recover at very different rates, and an electric or heat-pump cylinder usually needs more volume than these ranges give to cover the same back-to-back demand.
- Headcount stands in for peak-hour demand rather than measuring it. No fixture count, bathroom count, simultaneous-use scenario, shower flow rate or duration, and no bath or soaking tub enters the calculation, so two houses with the same number of occupants and completely different fixtures get the same answer.
- No water temperatures are entered. Incoming mains temperature falls in winter, storage set point and thermostatic blending change how much usable hot water a given tank delivers, and stratification breaks down before a tank is nominally empty — this is nameplate volume, not what you will draw at temperature.
- The bands stop at five occupants and describe a conventional storage heater. A household of ten returns the same range as a household of five, and heat-pump cylinders, solar-preheated stores and instantaneous units are sized on different grounds entirely.
- This is not an installation or compliance check. Tank size says nothing about the relief and expansion arrangements a stored hot-water system requires, scald protection at outlets, legionella control in storage and distribution, or whether the gas, flue or electrical supply can serve the appliance — those come from the code in force where the work is done and from the installer competence that code demands.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Rule-of-thumb ranges: 1-2 people need 30-40 gallons, 3-4 people 50-65 gallons, 5+ people 65-80 gallons
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