Measure the setup you will actually use
Start with a filled container and record the water level or volume. Run the complete schedule you plan to use for a day, then measure the change. Keep units consistent. If rainfall or refilling affects the tank, that trial cannot isolate system delivery.
Repeat under supervised conditions and record variation. This measures system output, not a biological requirement for every plant or a guarantee for hotter weather. Inspect root-zone moisture separately to establish whether the schedule is appropriate.
Record delivery and pot moisture during a supervised trial ↗
Calculate the planned draw
Multiply daily delivery by days between refills. Add a reserve percentage that reflects your own uncertainty. Then add unusable water: a pump intake may require a minimum level, and the bottom of a tank may not be fully accessible.
Illustrative example: 1.5 liters daily over seven days draws 10.5 liters. A chosen 25% reserve adds 2.625 liters. With one liter unusable, the total is 14.125 liters. These are example inputs, not a recommended dose or safety margin. Our calculator follows this exact formula.
Check usable capacity, not just the label
Read the manual for minimum water level, intake placement and operating limits. Plan refill access before filling a container that becomes difficult to move. Keep storage within building rules. The calculator cannot assess loading or installation safety.
A bigger tank cannot fix every failure
Heat, wind, plant growth and outlet changes can make a previous trial unrepresentative. A larger reservoir cannot fix a blocked dripper, dead battery or leak. Arrange backup checks for longer absences and leave a record of normal delivery for your helper.
Sources & limitations
These sources inform the background and system distinctions. The planning workflow is our editorial synthesis. We have not tested the named brands; model requirements and regional availability vary.
Links are currently ordinary, non-commissioned links. Read our commercial disclosure.
Turn the guide into a plan.
Choose a system or calculate a reservoir ↗