It can be difficult to determine how much yarn is needed for cast-on techniques like the long-tail or twisted German methods. Many knitters have pulled a length of yarn that they thought was long enough, and ended up running out of yarn well before they cast on the needed number of stitches. However, a number of techniques can help you discern how much yarn you need for these common cast-on techniques.
The Rule of Thumb of Three
Use the knitting rule of three. In the book “Knitting in Plain English,” author Maggie Righetti describes her “rule of thumb of three.” The rule is that it takes a tail of yarn approximately three times the length of the cast-on row to complete a long-tail cast on.
Knit a gauge swatch to help you estimate the length of your cast-on row. You will need to knit at least a 4-by-4 inch swatch to get an accurate reading on your gauge with the specified yarn and needle size. Note the number of stitches per inch that you get in your swatch.
Determine the cast-on length. If you are knitting from a pattern, look at the pattern schematics. The exact measurements for each section of the garment should be included in the schematics. Take the measurement for the section that you will cast on and multiply it by three. Add at least 10 inches to this number for the tail to be woven in later. For instance, if the measurement for a scarf is 8 inches wide, you will need 24 inches of yarn for the cast on and another 10 for the tail; 34 inches total.
Divide by the gauge. If you do not have pattern schematic with measurements, but you do have the pattern’s gauge and the number of stitches to cast on, you can do some quick math to figure out the length for cast on. If your gauge is 4 stitches per inch and your initial cast-on is 100 stitches, the approximate width of the initial cast on is 25 inches. You will need 75 inches of yarn for the cast-on, plus an additional 10 for the tail, for a total of 85 inches.
Wrap the yarn around the needle. Many knitters can estimate the length of yarn by wrapping it around the needle 10 times. Mark the beginning and end points of the wrap with your fingers, unwrap and measure. This should be the approximate length of yarn needed to cast on 10 stitches. Multiply by the number of stitches you need to cast on. For instance, if you wrap 10 times and use 4 inches of yarn, and your cast will be 100 stitches, divide 4 inches by 10 stitches for a total of .4 inches per stitch. Multiply .4 inches by 100, for a total of 40 inches of yarn for your cast on. Add an additional 10 inches for your tail, for a total of 50 inches.
Cast on and unravel. This method will give you an accurate estimate of how much yarn you will need. Cast on 10 stitches, and mark the beginning and end points of your yarn. Pull the stitches off your needle and unravel. Measure the amount of yarn that the stitches used, and divide by the number of stitches you cast on, in this case 10. Multiply that number by the total of stitches you need to cast on; add 10 inches for your tail.
Use two balls of yarn. Knitters can completely circumvent the need for estimating a length of yarn for cast-ons, by simply using two balls of yarn. Tie the yarns together in a slip knot, hold the two strands of yarn in your hand as for a regular long tail cast on, and begin. You will not run out of tail for your cast on. Simply cut the second strand of yarn, leaving yourself a generous tail to weave in, when you have completed the requisite number of stitches for the cast on.