Once you've got a sense of the prices that your art sells at (see previous answers), it can help to have a math equation that you use to price your works, so that your prices are consistent across your works (until you decide it's time to raise your prices). For those of you who are willing to wade through some math, I'll share the approach I use below.
I've been thinking about making some web-based software where artists can just enter the prices and sizes of work they've previously sold and it spits out a pricing equation for them to use for selling future works . I'd love to know if any of you think you'd use something like that.
Two commonly used pricing equations:
Typically, the bigger the piece is, the more it sells for. Here are two possible equations to choose from. I'm assuming your work is 2D.
Charge by area (square inches):
price = (width x height x factor1) + factor2
With this calculation, larger paintings cost quite a bit more than smaller paintings.
Charge by perimeter (linear inches):
price = ((width + height) x factor1) + factor2
With this calculation, larger paintings cost more than smaller ones, but not as much more as in the area equation.
What are factor1 and factor2?
factor1 and factor2 are just numbers that make the calculated price work out in the ballpark that you want to sell your work for.
factor2 should reflect the minimum that it's worth selling a work for, no matter how tiny the work is. So if even tiny works take you two hours to make, and cost $10 in supplies, then figure out what you want to earn per hour (say $15/hour) and multiply that by how long it takes you to make the tiny work (2 hours), and add the cost of supplies, and you get 40 for factor2. That's (15 x 2) + 10. Of course it also needs to take into consideration how much someone will pay for your small work.
factor1 should reflect how much longer it costs you to make a larger work , and how much more the materials cost, and also how much more clients are willing to pay for larger works. This one is trickier to calculate. What I do for that is choose four works of different sizes that sold for prices I was happy with. Then I work out what factor1 would have been for each. Then I take an average of the different factor1's I got and use that for my equation for pricing future works.
How to calculate factor1 for your previously sold works depends on which of the two equations above you go with. Let's assume you came up with 40 for factor2. (You need to work out factor2 first.)
Charge by area: factor1 = (price - 40) / (width * height)
Charge by perimeter: factor1 = (price - 40) / (width + height)
For each of the four previously sold works, I plonk the width, height and price into the desired one of the equations above and calculate factor1. Odds are that factor1 will turn out differently for each of the four works. So then I average the four values of factor1 as follows:
factor1 for future price calculations = (factor1(#1) + factor1(#2) + factor2(#3) + factor1(#4)) / 4
Let's say I wanted to use the perimeter equation and I came up with 2.32 for my factor1... My final equation would then be:
price = ((width + height) x 2.32) + 40
So a 10x10 inch painting would be (2.32 x (10+10)) + 40 = (2.32 x 20) + 40 = $86.40
And a 24x24 inch painting would be (2.32 x (24+24)) + 40 = (2.32 x 48) + 40 = $151.36
Hope this turns out to be useful for someone!