Compost Bin Design
Compost bins are containers that you fill with organic matter to give it an opportunity to break down into compost. Compost and the process of making compost is an essential part of the management of any garden, so the design and construction of your compost bins should be one of the first things you do when setting up a food garden.

The same basic principles outlined in the Garden Zones Section also apply to picking the best site for your compost bins.  However, as well as considering distance from your back door, you should also be mindful of the distance to the main vegetable patch as it is usually the main generator of  green waste.  Carting this  material even a few short metres to your compost bins will add a lot of extra work over a year.  So if you are not running chickens I recommend that your bins be placed in or right next to your main vegetable patch.  Which, if you are applying Garden Zones principles will also be reasonably close to your back door.

A small aquarium will have much higher fluctuations in water temperature then a large one as small amounts of water are much more prone to temperature variations.  Ph and ammonia levels will also tend to fluctuate more.  Similar principles apply to compost bins.

Small bins will dry out more quickly and are subject to greater temperature variations outside of the heat generated from the composting process.  This in turn discourages worms and can kill the beneficial microbes that break down organic matter, thereby slowing the whole composting process down and producing a poorer quality finished compost. 

It's been my experience that the minimum size for an effective compost bin is around 90 cm²  (3 ft²) and having bigger bins then this only improves the quality of the finished compost.  However there is an effective maximum size for any garden as if the bins are too large you may not have enough waste to fill them.

Number of compost bins
The process of composting involves filling a bin with all the available green waste until it is full to overflowing.  The bin is then left to stand for three to six months, with an occasional turn over with a garden fork.  By then it should have broken down into a friable material not unlike coarse soil, which is ready to spread on your garden. So in order to give a compost bin enough time to fully break down the organic matter you will need two and preferably three compost bins.  Whilst one is being filled the other one or two bins are in various stages of breaking down their organic matter or being emptied in preparation to be filled up again.