Every yarn has a gauge (also known as a “tension”). This number refers to the number of stitches per inch. Every pattern will tell you what gauge of yarn to use for the project; make sure you utilize the correct gauge or your final product will come out looking completely different from your pattern.The gauge does not reflect the size of the completed garment.
To measure your yarn’s gauge yourself, count the number of stitches over 6 inches (15cm), then divide that number by 6. Your answer will determine the gauge of your yarn.
Just because two different yarns share the same gauge does not mean they will function the same within the confines of a pattern. Texture, drape, fiber and other factors also affect on the final outcome of your project.;
, Certain yarn weights perform better with certain projects. Lace or cobweb is best to make doilies. Fingering works best to knit socks. Sport is ideal for making baby clothes or blankets. Worsted is used to make blankets and sweaters, and bulky is perfect for scarves and rugs.When working with different yarn weights, make sure you also use the correct needle size and hook size for that yarn.
When looking at weights, double check that you are also using the recommended brand for your pattern of choice.
 When selecting your pattern, decide how you want your finished piece to hang. Depending on whether you prefer flowing or more structured, select your yarn accordingly.For a very dense drape, select a very thin yarn.
For a more relaxed drape, select a thicker yarn and use large needles to create large stitches.
 Most patterns recommend working with a specific yarn and it's important to take this seriously. Using the wrong yarn can completely alter your pattern, and since different yarns have different elasticities, you may find yourself running out of yarn altogether.To avoid running out of yarn, buy extra. Most yarn stores have a flexible return policy, and if not, you can always use your extra yarn in another project.
If you are going to substitute yarn, make sure you replace your yarn with a yarn of a similar elasticity. Inelastic yarns include silk, linen, hemp, alpaca, tencel, bamboo, cotton and rayon.
Choose your yarn based on gauge.
Choose your yarn based on weight.
Choose your yarn based on drape.
Choose the yarn recommended by your pattern.
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