I wondered how big my physical, not digital, art work should be for a finished book size 6.5 x 6.5? Many thanks
You forget to tell which unit you mean, but I guess you mean inches. (Most users here from outside USA measure in metric units.)
Anyway units doesn't really matter. The answer is that it's up to you. It all depends on the media you are using, your personal style and which expression you want the final print to have. Your question doesn't reveal any details about this, so I can only give you some general advice.
Drawing smaller than the finished size. In some cases this might be the right choice, but I wouldn't recommend it. Scaling up a small work of art will reveal every single error and inconsistency in the technique and might end up looking a little amateurish. It will also bring unwanted attention to the paper/canvas texture and it will get a kind of "digital" quality if it's obvious that it's larger than the original.
Drawing to scale. Might be fine if your technique is good enough. Can look as if the artwork was made "directly in the book" and can bring attention to the fact that it's "handmade" which is good if that is what you are trying to achieve.
Drawing larger than the finished size. This is probably the most common choice. Scaling artwork down will camouflage errors and unintended wobbly lines. Everything will look a bit cleaner and sharper. If the scanner you are going to use isn't high-end a 1:1 scan can look a little blurry. This is less of a problem if the artwork is scaled down. Many comic book artists create their originals at perhaps 125%-200% of the finished size. You should of course be aware that your lines will be thinner and it might take some trial and error to find a good combination of scale and technique.
If you have access to a scanner I would recommend to do some experiments with scanning and printing artwork in different sizes.
Besides the scale there are a few things you should be aware of:
- Don't draw to the edge of the paper. Use a piece of paper which is larger than you need, so there can be a clean margin around your drawing. This makes it easier to scan and crop digitally.
- If your artwork is to be printed to the edge of the paper you should make sure to have about 0.125" bleed or more on all four sides (when scaled to the final size!). Bleed is just a continuation of your artwork which will be cut off after print. Furthermore you should be aware that the finished page might be cut a tiny bit off-center, so don't have important details too close to the edge.
If you wish to have art go off the pages, or print to the edge of the pages, then you need to add at least .125" to each side - or increase the art by .25" in both width and height. Realize that extra eighth-inch will be trimmed off each side during production.
Otherwise, if art is not to print to the edges.. whatever size you want.