This article is about math (an editor disclaimer, before becoming an editor for BellaOnline I was an accountant so numbers are my friends). Learning some or relearning some is necessary if you need to alter an existing pattern to fit a shape or size that isn’t included in the original pattern. One thing you may want to try before attempting to adjust the pattern is to try knitting a gauge swatch using larger or smaller, needles or yarn, than what is called for in the pattern. Using larger needles and larger weight yarn will make the article bigger, but it will also affect how the garment will drape and flow. Using smaller needles and smaller yarn will make the garment smaller, but again it will affect how the garment will look and drape. If you like the way the swatch looks and feels you will have to do some math to make sure it will fit, but you will be able to use the pattern as written to finish the garment.
One example of how using a larger needle will make a sweater bigger is: Assume the pattern calls for worsted weight yarn and size 8 (U.S.) needles to achieve a gauge of 4 stitches to an inch, if you go up a needle size to size 9 needles you might get 3 1/2 stitches to an inch. Further assume you are casting on 80 stitches, if you are knitting 4 stitches to the inch and you cast on 80 stitches that pattern piece will measure 20 inches. If you cast on with larger needles and get a gauge of 3 1/2 stitches you will get a pattern piece that measures 22.8 inches or an increase in size of nearly 3 inches. If that piece is the front and you do the same for the back, the garment will be nearly 6 inches bigger in total. Conversely if you use smaller needles and get a gauge of 4.5 stitches in an inch that will reduce the finish pattern piece to 17.7 inches (still assuming 80 cast on stitches) or a decrease of nearly 2.5 inches in just one piece. The beauty of this method is that you will still be able to use the pattern and all of the respective increases and decreases.
Now if that doesn’t work for you because you don’t like the way the design looks or the drape of the fabric. Then it is more complicated, but still possible. Let us assume you are still working with a pattern that calls for 80 stitches to be cast on and the gauge attained should be 4 stitches per inch. That would be a 20 inch finished piece 80 stitches divided by 4 stitches per inch equals 20. If you needed that piece to be 30 inches instead, you would have to cast on 120 stitches, or in other words 4 stitches per inch times 30 inches equals 120 stitches. The tricky part is how many to increase or decrease when the pattern calls for that. Each pattern will be different, but often patterns will say something like, “When you have knit evenly for 10 inches, it is time to start increasing at the beginning and end of every other row five times, or until you have 90 stitches on your needles.” This will increase the piece by 2 1/2 inches. Remember you have started with 120 stitches so you will need to increase until you have an additional 2 1/2 inches or 9 more stitches because 2.5 inches time 3.5 stitches in an inch is 8.75 (rounded up to 9) so you will only increase your stitches to 129.
Although this may seem complicated, and it is a bit, you want to check your math a lot before attempting to do this. If you remember the basic:
Stitches per inch or centimeters X Size = Number of stitches needed
Number of stitches called for in pattern ÷ Stitches per inch or centimeters = Finished size of piece
You will have the building blocks for starting your pattern adjustments. As a final note, the pattern publisher or designer may be able to help with making the adjustments since they may use clever software designed for this purpose. And most yarn shops will also help you do the math if you are buying the yarn or pattern from them. Good luck and happy alterations.