“8 x 10″ is pretty small so you could just make the thumbnail 4″ x 5″ if you wanted to make the thumbnail smaller again you could make it 2″ x 2 ½ “ All I’m doing is halving the dimensions each time, so proportions are staying the same.
Just divide your painting proportions by a convenient number it wont always be a half.

Dave.

I was having A LOT of trouble with this exact same issue myself. I finally figured out a great way to deal with it. This works great for me.

I use an image editing software called GIMP. I’m sure this would work the same in Photoshop or a similar program. I use GIMP because its free and I use a Mac.

Anyways, I create a new file in GIMP, and make it so that the size of it is the same size as my canvas. Then, I open up the image I want to paint as a new layer on top of the blank image. Then I adjust the size of this new layer until it fits on top of my canvas how I want to paint it. Then you can print it out so that it is smaller than your canvas, but still has the same relative dimensions.

I hope this makes sense to you, good luck!

Draw an 8X10 inch box on a piece of paper. Draw a diagonal line from one corner to the the other. Anywhere along the the diagonal will match — proportionally — your 8X10 final size. You make a mark on the diagonal, then use a T-square to lightly lay an horizontal line and a vertical line, and there is the size of your study size.

I think you’ve got it already, but maybe this can help too. 8 is 80% of 10. Or 0.8 out of 1.

Next pick the longest side for your next scaled version. If that is 2 inches, just multiply the longest dimension by 0.8 to get the shorter side.

And you’re done.

Adam