Things You'll Need
Paper and pencil
Knitting patterns use standard garment sizes, but most people do not have standard bodies. If you can do a few simple math calculations and take accurate measurements, it is easy to make a knitting pattern large enough to fit you.
Take your measurements. Get accurate measurements of bust, hip and upper arm circumferences, shoulder width, shoulder to waist length, and sleeve length. If you are planning a garment for yourself, get a friend to help with the measurements.
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Consult the pattern schematic, which is a graphic representation of all the garment pieces that shows the finished dimensions by size. Compare your measurements to the the schematic and note the differences. For example, if the largest waist size is 30 inches and you need 35 inches, the difference is five inches.
Determine the stitches per inch from the pattern's gauge requirement. For example, if the gauge is 24 stitches over four inches, the per-inch stitch gauge is six.
Use the stitches-per-inch figure to determine how many stitches you need to increase. For example, to increase the waist five inches at a gauge of six stitches per inch, you need to add 30 stitches to the finished piece at the waist. Make these calculations for all the measurements.
Update the pattern instructions with the new stitch counts. In pieced garments, split the increases among the pieces. For example, to add 30 stitches to a pullover, add 15 stitches to the front and the back.
Knit a gauge swatch to make sure your finished sweater will fit. Take the time to wash and dry the swatch. Cast on for your custom-fitted sweater and knit away.
If you are using a European pattern, take measurements in centimeters.
If you do not know how to take body measurements, look for instructions in a general knitting book, like "Vogue Knitting: The Ultimate Knitting Book."