Grading a pattern is a way of sizing a pattern up (or down) while maintaining the proportions of the original pattern. Learning how to grade a pattern is a useful skill to have if you enjoy working with vintage patterns or have a favorite pattern that is now a size or two too big (or too small).
Grading patterns can be relatively simple. The "cut and spread" option is one method for pattern grading. Begin by tracing your original pattern. I traced my pattern on to white butcher paper. You can also cover the original pattern with transparent paper and trace that way (look for Swedish tracing paper or exam table paper, like the kind in a doctor's office; easily found on Amazon.com). Fusible interfacing will also do in a pinch. If you have an uncut pattern to grade, you can use dressmaker's carbon and a tracing wheel to transfer the pattern to paper. Be sure to transfer all markings, darts and grain lines. Labeling your pattern pieces as you go will help you keep things straight.
After you have your traced pattern cut out, it's time to do a little (easy!) math. In my example, my original pattern fits a 32" bust, but I want to make it two sizes larger, to fit a 36" bust. That's a 4 inch difference. Since the pattern has a front and back (like most patterns), I divide the difference by 2. In this example, 2" is the grade for the entire front (or back) of the pattern. If the pattern splits a piece (like the bodice) into halves (left and right), you'll need divide by 2 again. In this example, that would result in a 1" grade for each piece of the bodice front. This is the pattern grading scale, or grade.
Next, you'll need to divide the grade by 3. This will give you the measurements for your spread. It's best not to get hung up on dividing exactly evenly (one of the measurements can be slightly larger than the others), just as long as the total is equal to the amount of your grade. For a 1" grade, the numbers might look like 1/4"-1/2"-1/4". Be sure to keep track of the measurements, as you'll want to duplicate them exactly for any other pieces in the bodice.
Draw three vertical lines on your traced pattern to indicate where you will cut in order to spread the pattern. Good places to draw these lines are from underarm to waist, shoulder to waist and neckline to waist.
Once the pattern is cut vertically, spread the four pieces the appropriate amount. I used transparent tape to keep the pieces of the pattern together.
Next, it's time to retrace the pattern. Be sure to transfer all markings, darts and grain lines again. Repeat the process, maintaining the same grade, as needed for any other pieces.
If your original pattern is too small, as opposed to too big, you will follow the same process. Determine the size difference in the same method outlined above. Instead of spreading the original pattern after it has been cut, overlap the pieces the appropriate amount. If you needed to size down 2", you would overlap the pattern pieces by 1/2"-1"-1/2". Retrace the pattern and transfer all markings.
Shifting is another simple method for pattern grading. The first step is to determine how much you need to grade your pattern. If we take the example of a bodice again, you might need to grade a 34" bust up to a 36" bust. That's a difference of 2". Again, divide the difference by 2 since we are only dealing with either the front or the back of a garment at one time. Divide again by 2 if the bodice is in two pieces. In this example, that equals a 1/2" grade.
Next, take the original pattern (you don't need to make a duplicate of the original pattern because we won't be cutting it up) and place it on top of a piece of paper. Trace the bottom and center edges.
Shift away from your traced line by the amount of your grade (in this example, ˝"). If you needed to grade down, or make your original pattern smaller, you would shift toward your traced line by the same amount. Trace the outer edges of the original pattern. Your traced lines will not match up exactly, of course, so blend together as best as possible. Transfer any markings, darts or grain lines and repeat for your remaining pattern pieces.
It's important to note that grading a pattern will not accomplish the same results as altering a pattern. Altering a pattern is the only way to make it conform to your exact measurements, particularly if your bust and hip measurements fall into two different sizes. To learn how to alter patterns to fit your body perfectly, check out Craftsy's Sew the Perfect Fit class. Or view the Plus-Size Pattern Fitting and Design class, which addresses fit issues for plus-size women. Even when dealing with an even grade (grading a pattern by the same amount all over), you will probably still have to make some minor fit adjustments, but grading the pattern will get you close to where you need to be.
If you're interested in learning more about pattern drafting, check out Craftsy's Jean-ius! Reverse Engineer Your Favorite Fit class.
Have you had success grading a pattern?