Water Tank Size Calculator
Find the right overhead or underground water tank size for your home. Enter your family size, daily water use, storage days and any extra use, and get the total storage needed in litres and gallons with a suggested standard tank size.
Calculation Breakdown
| Step | Value |
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How to use
- Enter the number of family members and the average water use per person per day.
- Set the number of storage days (3-7 days is common for areas with supply gaps).
- Add extra daily use for garden, cleaning or pets, and the suggested tank size appears instantly.
How the tank size is calculated
Step 1: Daily household use = family members x per-person use + extra use. Step 2: Total storage needed = daily household use x storage days. Step 3: Convert to gallons — US gallons = litres / 3.785, Imperial gallons = litres / 4.546. Step 4: Round UP to the nearest standard tank size (500, 750, 1000, 1500 or 2000 litres), because rounding down would leave you short. If the need is above 2000 litres, use two or more tanks. Tip: allow a small reserve for hot days and unexpected guests instead of sizing to the exact need.