Well the container doesn't have that info on it from what I can see so I just took some measurements. The diameter is 9.5 inches and the height is 10 inches. So based on dimensions the volume is only roughly 3.5 gallons. Sounds about right since you can easily put one of these in a 5 gallon bucket. Perfect for a single small plant with some good soil and steady fertilizer I suppose being indoor and all, and easy to throw back into the compost at the end of the season.
Of course I'm sure using an 18 gallon self watering type of container would be far better, giving roots much more medium to grow in, and using a fertilizer strip method on the top of the soil, allowing the roots to know exactly where the fertilizer is when they need it. I'm going to build one of those soon. But this I would say the easiest and cheapest self watering type of contraption you could manage. In fact if you really wanted to you could cover the top with plastic after placing a thin strip of fertilizer away from the root base near the edges of the container on top of the soil. May be too close though due to such a small container.
