How to use a Proportional Divider in Art

How to use a proportional divider, how to use a proportional scale divider, how to get an accurate sketch, how to get accurate sketches, how to get better at drawing

This is a post for those of you that draw or paint and find it tricky to get a good sketch before you begin painting/adding colour. This is one of the areas I’d like to improve upon so I think this method is helping me get more accurate and highlights where I’m going wrong.

Here is the video that goes with this post in case you prefer to watch rather than read! :

Firstly I have to say that there are various other ways you can get a good sketch; Some of these include : 

  • Trace through a light box drawing board or tracing paper
  • Use carbon paper (very carefully!) or some of the newer papers (such as Tracedown)
  • Free hand drawing
  • Use the grid method
  • Various gadgets and apps you can get – which somehow don’t appeal to me

My free hand drawing is OK but I’m not yet happy enough with my accuracy to produce good enough likenesses in work where this is important e.g. portraits. I also tend to scale my work up from the reference photo frequently so tracing isn’t really going to work very easily and I find that the grid method doesn’t help me improve my accuracy. So to help me improve and and to create accurate sketches I currently use a proportional divider in my art. 

proportional divider, proportional scale divider, How to use a Proportional Divider in Art

Proportional Scale Divider – What is it?

So what is a proportional scale divider or proportional divider? It’s a little widget similar to a compass. it has 2 arms the same length which are joined. You use one end to measure your reference photo and the other end to measure your target sketch. If the arms are joined in the centre then both sides are equal in length meaning that when you seperate them out the distance between the arms is the same at both ends. You can use this to exactly copy a reference photo i.e. to the same scale. If you move where the join is then this can be used for scaling up/down because the distance between one set of arms will be shorter than the other side. 

There are lots of different models on the market. I started off with a plastic cheapish one but I found that it kept slipping and one side wasn’t very accurate as the edges were blunt so not very useful for portaits!

I then bought a more expensive snazzy nautical one and I love this one – both sides are sharp so very accurate and the centre join tightens up really well meaning it doesn’t slip much. The only thing to watch with this model is that they can sometimes mark the paper so you have to be careful not to get little dot indents everywhere.

Proportional Scale Divider – How do you use it?

This is how I use one – I’m not sure if there is a more ‘correct’ method but this works for me 🙂 

I usually draw a horizontal and a vertical line across the centre on my reference photo and my target sketch paper. This is so that the centre cross will act as a point of reference in both the reference photo and drawing. I then use this central point to plot all the other points : 

Draw a horizontal and vertical line across the centre of your target sketch paper Draw a horizontal and vertical line across the centre of your reference photo

Next you will need to move the join on your proportional divider to your requirements. If you are scaling 1:1 then move it to the centre so that when you open it the arms are the same distance away from each other on both sides. If you are scaling up then move the join on the arms along so that the smaller end can accommodate your reference photo and the larger end will fit on your paper.

Next pick a point on the reference photo (I usually start at a point on the horizontal line) that you would like to mark. In this example I am marking the centre point of the paper where the two lines meet to the edge of the bees head which is on the horizontal line with the shorter end of my divider.

Next I turn my proportional divider over and mark the same point on my drawing paper (notice I’m scaling up to roughly double the size).

I then do this a few more times with the outline of my subject along the horizontal and vertical lines :

Then I start picking out reference points on my photo – in this example I started with the edge of the bees head.

I then measure the distance up from the horizontal line and make a little mark (A) and then the distance across from the vertical :

In this last step I draw my horizontal point at the same distance up as (A) above.

I then repeat this process on various points on the drawing.

The last bit is to join up all the little points to create an outline. If you are fairly confident then you will need fewer points. If you are a beginner then its worth taking your time and creating a lot of points close to each other.

And that is pretty much it. If you have a very complex drawing then this process can take quite a long time. but for simple drawings such as this bee it’s a fairly quick process but means that you will get an accurate scaled up sketch!

I hope you have enjoyed this post about how to use a proportional divider and please comment below if you have any questions!

Let me know if there is a specific topic you would like me to cover in these blog posts!

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