The most common size I am using lately is 6 x 6". Yes, that's inches! Sometimes I paint a little bigger, but that will always be described underneath the photo of the painting when I post it. I use light fast acrylic paint, which dries hard to the touch very quickly, then before varnishing, I take the photo that will be published on the web. Varnishing adds another layer of protection, but it can be tricky to photograph because of the "sheen".
The finished canvas can be hung directly on the wall without any matting or framing, or it can be displayed with a tiny easel anyplace a spot of color is desirable.
Here's the rooster, with a measuring tape showing it's size. This painting has already been varnished, and you will notice the little bit of shine in the upper left corner.
Here's the back side. The canvas wraps around the wooden support and is secured with staples. The sides are 3/4" deep, and I paint and varnish them to match the front.
This is a sample of how they look on the wall. The 6 x 6 canvases are so light weight that I just stick sewing pins into the wall and hang the painting by resting the wooden framework on top of the pins. The canvas sits flush to the wall for a very contemporary look. No mats, no frames, and they look so cute! The framed artwork in this photo is one of my pastels, which is framed behind glass for protection. Any questions? :)