Hot Water Tank Volume Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 10/10/2026
The recommended hot water tank volume depends on the number of occupants: about 50 to 75 L for a single person, 150 to 200 L for a household of 4, and 200 to 300 L for 5 or more.
Explanation
Choosing the right domestic hot water (DHW) tank volume is a balancing act: too small a tank forces you to wait for water to reheat between closely spaced showers (or worse, run out of hot water mid-use), while too large a tank heats and keeps hot an unnecessarily large volume of water, wasting energy through constant heat loss. Usual sizing benchmarks, which increase with the number of occupants but at a decreasing rate (the need per person slightly drops in a larger household, as usage overlaps more), range from about 50 to 75 liters for a single person up to 200 to 300 liters for a household of 5 or more. These benchmarks remain rough orders of magnitude, not strict rules: actual consumption habits (long or short showers, frequent baths, a dishwasher or washing machine connected to hot water) make the real need vary around these ranges. Once this volume is chosen, you still need to determine the heating power required to heat it within a reasonable time: see our water heater power calculator, which takes this volume as its starting input. The volume stored in the tank is generally kept at a higher temperature (55 to 65°C) than what's actually used at the tap (around 40°C), meaning a 200 L tank actually delivers somewhat more than 200 L of usable water once mixed with cold water at the mixer tap.
Example: a household of 4
Inputs
Number of occupants: 4.
Calculation
According to usual sizing benchmarks, a household of 4 falls in the 150 to 200 L range.
Result
A hot water tank of 150 to 200 L is generally recommended for this household.
Frequently asked questions
Why does the need per person decrease in a larger household?
Because hot water usage in a larger household overlaps more over time (several people rarely use a shower at exactly the same moment, but the tank has more time to reheat between spaced-out uses), and because some usage (dishwasher, washing machine) doesn't directly depend on the number of occupants. That's why the recommended volume per person slightly decreases as the household grows, rather than increasing strictly proportionally.
What happens if my tank is too small for my household?
The most common symptom is running short of hot water at the end of the day or during closely spaced uses (several showers in a row, for example), the tank not having had time to reheat between draws. It's not dangerous, but it's uncomfortable day to day; in that case, a larger tank or a supplementary instant water heater can solve the problem.
Do these volumes also apply to a solar water heater?
The same general orders of magnitude apply, but an individual solar water heater instead uses a benchmark of 50 to 70 liters of storage per person, slightly different from a standard electric water heater, since its sizing also depends on the available solar collector area and local sunshine — see our domestic hot water cost calculator to compare how this choice affects the annual bill.