Our buckets have a 15 litre capacity and they are 42cm high and 25cm square.
People usually find they need a second bucket because they're filling the 1 they already have in 2 weeks or less. And this means they have to wait an additional 7 to 10 days while the Boost finishes its magic and completes the fermentation process (remember, you, and your garden only get maximum benefits when the process is fully complete). So, rather than stop composting all together, a 2nd bucket means you can make a "career of continuous composting" and have a garden and veges that will love you forever. Here's a detail shot of the bucket lid (all the Bokashi magic happens under it).