Water-storage planning
Garden Water Tank Size Calculator
Estimate usable and nominal tank capacity from daily irrigation demand, desired autonomy and reserve.
Size storage from demand and autonomy
Daily demand multiplied by days of desired storage gives the base usable volume. Reserve protects against uncertainty, while the usable-share input accounts for dead storage and operating limits. The nominal tank is therefore larger than the water you plan to withdraw.
Storage is only half of the water balance
A tank must also refill fast enough. For rainwater systems, compare roof catchment and seasonal rainfall with garden demand. For pumped storage, compare refill flow and available pumping hours. Overflow, first-flush diversion, freezing, algae control and local requirements affect installation.
Estimate demand with the garden water demand calculator and pump requirements with the TDH calculator.
Frequently asked questions
Should I buy the exact calculated size?
Usually choose the next practical size above the result after checking space and structural support.
Does tank capacity equal usable capacity?
Not always. Outlet position and operating rules can leave unusable volume.
How heavy is stored water?
Water is heavy, so the base and supporting structure must be designed for the full tank load.