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Water Heater Sizing Calculator

Get a rule-of-thumb recommended tank size (in gallons) based on household size.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-25 · v1.0.0

Market
Imperial · sales tax

Recommended tank size

57.5 gallons (recommended)

Check your inputs

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 (GPM) instead.

Recommended range, low
50 gal
Recommended range, high
65 gal

With the figures above, the recommended tank size comes to 57.5 gallons (recommended). The method behind this is well established, though site conditions and material batches will move it somewhat. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

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.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Rule-of-thumb ranges: 1-2 people need 30-40 gallons, 3-4 people 50-65 gallons, 5+ people 65-80 gallons

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Still deciding? Tankless vs Tank Water Heater — the factors that actually differ, with no invented prices.

Frequently asked questions

Should I get a tank or tankless water heater?
This calculator addresses tank sizing. Tankless units are sized differently — by flow rate (GPM), adding up the fixtures you'd realistically run at once (a shower is about 2.5 GPM). Most 3-4 person homes need an 8-10 GPM tankless unit.
What if I have a lot of bathrooms but a small household?
Size toward the higher end of the range for your household size, or consider a tankless system, since simultaneous-use capacity matters as much as household size.
Does climate affect sizing?
Yes, for tankless units especially — colder incoming groundwater temperature reduces a tankless unit's effective GPM output, so homes in cold climates often need a larger unit than the same household size would need in a warm climate.