How to use a proportional wheel -
Images courtesy of John Pototschnik

For every painting workshop I’ve taught since the 1980s, I’ve always listed a proportional wheel as one of the items on the art supply list. Ninety percent of the time students came to the workshop empty-handed, asking “What’s a proportional wheel?” I learned quickly to always have an abundant supply on hand for them to purchase.

A proportional wheel (also known as a proportional scale) is a very useful tool and a significant time saver when determining if a preliminary sketch and the canvas selected for its enlargement are of the same proportion.

Why is this important? Through my years of teaching I have found some students give little attention to this important detail. Typically, after creating a sketch and deciding to use it as the basis for a painting, they will go to their closet and pull out a canvas … any canvas. Often the canvas will not be proportional to their sketch, thereby nullifying the sketch.

Think of it this way: if the sketch or field study is one proportion, say 4.5″ x 6″, and the canvas selected for enlargement of the sketch is a 16″ x 20″, based on the wheel below, some of the sketch will have to be left off, as it will not fit on the canvas. Hence, the composition will be changed and the sketch somewhat nullified.

What is a proportional scale

How does a proportional wheel work?

First of all, notice that there are two rotating disks, the smaller disk (Size of Original), and the larger disk (Reproduction Size). For the purposes of this instruction, forget the labels and just concern yourself with the numbers, 1″ – 100″, on each of the disks.

The beauty of this tool is that once the applicable numbers are lined up, everything around the wheel is proportional to those numbers. Let’s use the example mentioned earlier. If your sketch/field study is 4.5″ x 6″, what size canvas should be selected in order to accommodate 100% of the sketch? The illustration of the wheel above gives the answer.

Continue reading at to learn more about how to use a proportional wheel.


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  1. Coincidentally, I used a proportion wheel on the very same day your article was published in PleinAir Today. It’s one of two I’ve had since my days in graphic design. It was essential then for image sizing, just as it is today. Today I used my wheel to experiment with various-sized enlargements for my next studio pastel painting. Thank you for writing about this invaluable tool.

    • Like you, Jude, I consider it an invaluable tool. Even though modern devices will make these calculations for you, I still prefer this device.

  2. If you don’t have a proportion wheel you can use a calculator. Target size divided by original, times 100 equals the percent of enlargement or reduction (Ie: target size is 21” and original size is 6” – 21/6=35×100=350%) (Ie: target size is 7.5” divided by original size of 40” =.1875 times 100 =18.75%)


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