With plein air season approaching, I decided to create a chart that would help me make thumb sketches for the more common standard size painting panels. I buy and pack lots of standard sizes for plein air events for the convenience of it and because standard size frames are much more affordable.
Many artists use a small sketchbook to make preliminary sketches on location before painting. I almost always allow time for this—it makes a huge difference when I work out the kinks in composition before starting to work in color. I keep a 5.5x8.5" wirebound sketchbook in my pack; I'm not picky on brand since I only use it for preliminary studies.
After doing really loose sketches for a while, I thought it would be helpful to create compositions a bit more carefully with my panel sizes in mind. I've traditionally just 'guesstimated' the size of a thumb sketch, but it's never right on the mark—and I don't really want to fuss with a ruler or anything that'll add weight to my pack.
After a little time with a calculator and Adobe Photoshop, voila!...here's my printable guide for some common sizes, plus some that I might make when I finally start preparing my own panels. I thought I'd share it in case anyone else found it useful. Truth be told, I did a little googling to see if anyone else had published something like this before I dove into Photoshop. (No dice.)
Printable Aspect Ratio Guide - PSD (only for those who want to edit in Adobe Photoshop)
If you print it at 100% size, it fits neatly within a 5x8" sketchbook. You can size it up or down depending on the typical size of your field studies.
To use it, I've cut it along the outside lines and can make hash marks along the edges of my intended panel size (note the square sketch behind the printed guide in the photo above). Of course, I always have to option to change it partway through a sketch if I wind up thinking a different aspect ratio would work better.
Hope that helps! Happy sketching—and painting.