Calculating How Much Stained Glass You’ll Need

Ashley Christensen
March 7, 2023

As anyone who has ever undertaken a project, large or small will tell you, there is nothing more frustrating than starting a project, only to discover you don’t have enough material to finish. This then means you have to find a stopping point, figure out what you still need to finish, and then make a trip to the store to purchase the necessary supplies. 

Ensuring you have the right amount of supplies before you begin a stained glass project is critical to ensure that all of your pieces match, and you don’t end up settling for using pieces that don’t quite match. If you’re lucky enough, some patterns will break it down for you, telling you exactly how much of each color will be required to complete the project. In case your pattern doesn’t tell you, or you designed your own pattern, here you’ll learn two different methods that will help you to calculate precisely how much stained glass you’ll need to purchase before you begin your next project. 

Color Method

Start by coloring your pattern with the desired colors for each piece. This will help you to visualize what colors you’ll need, and roughly how much of each color. Once you’ve colored your whole pattern, figure out the approximate size of each piece. You’ll need to determine the overall square foot size (multiply the width by the height) of your entire project. Once you’ve determined the square footage, add an additional 20-30% for waste and breakage.  

Once you have figured out the total square footage of your project and added the additional 20-30%, it is time to determine how much of each specific color you’re going to need. Start by visually determining a rough percentage of each color, for example, 50% green, 40% red, and 10% white (all together need to equal 100%). Now that you have your approximate values for each color, divide the total area plus the extra by the percentage you’ve figured out for each color. This number will then give you the amount of stained glass you need for each color in square inches. To convert this number to square feet, divide it by 144. 

Drawing Method

This method can be easier to help you determine how much of each color of stained glass you need, but it can be more time-consuming. This method is often preferred by those who aren’t a big fan of doing all the math calculations, this method is more of a visual estimate. 

Start by laying your pattern out on a work surface. You’ll then need to cut tracing paper or scrap paper, into a number of 12 X 12 squares. Start by having one square for each color in your pattern, more squares may be required for larger patterns that use a lot of one color. Once you have all your tracing paper cut out, simply trace each pattern piece onto the tracing paper according to its color, (all the white on one piece of paper, all the green on another, and so forth). This will give you a visual idea of how much stained glass you will need for each color in your pattern. Don’t forget to add an additional 20-30% for waste and breakage to ensure you have enough to complete your project. 

With either of these methods, you should have a pretty good indication of how much stained glass you need to purchase before you begin your project. Knowing how much to purchase should help you from having to stop mid-project and go buy more and hope it matches.

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