When working with knits, it is important to know the percentage of stretch your particular fabric possesses. If a pattern calls for 50% stretch and your fabric only has 25% stretch, there will be problems with fit! I learned this the hard way when I made a swimsuit out of Qiana when I was in high school. It turned out great but I couldn’t get it on.
Most patterns for knits will have a knit gauge (or Pick-A-Knit rule) on the back of the envelope as on this Simplicity pattern:
Other patterns will simply give you the percentage of stretch required. Yet others will give you both – as on this Kwik-Sew pattern:
To make it easy to figure the percentage of stretch, I have taken an old school ruler and made my own gauge. Using 5″ as the base, I have marked off every half inch beyond that in 10-percent increments. Easy, cheap and very handy for those of us who love to sew and wear knit fabrics. With this ruler I can gauge knits up to 140% stretch (12″ mark) although my scanner cut that end off so you can’t see it here.
Simply begin with a 5″ piece of fabric (I prefer to use a folded piece because the cut edges tend to be more stretchy than the body of the fabric) and see how far you can easily stretch it. If your fabric has more stretch than the pattern requires you will want to go down in size (or plan on taking the garment in during fitting), if your fabric has less stretch you’ll want to size up or add extra-wide seams.