I've been doing some tiny canvasses for my Etsy shop - and coincidentally, so has Sarah! (hers are gorgeous check out her blog ) We both posted at the same time and had both chosen 4 inch squares, though hers are on wood panels and mine are on canvas.
These are 4 inches square, on deep 1.5 inch sided, gallery wrapped canvas.
They work well in a group and even look nice standing up on a shelf as they are so deep.
I really enjoyed doing them and for a change used acrylics, not my usual choice of medium but it worked well for me.