Calculating Yarn Requirements (tank used in example)
From my experience, this is one of the most common knitting questions. The amount required depends on the weight of the yarn, needle size, and the stitch pattern(s). As you gain experience, answering this question becomes easier.
At the beginning, we rely on the quantities provided in pattern instructions. But instructions give quantities for the brand used by the designer of the project. Being able to purchase the brand used in the instructions is simple and makes life easy. Sometimes it’s not possible to find the yarn asked for in a pattern, so a substitute is necessary. Substituting yarn is not simply a matter of replacing one ball for another (refer to my e-book “It’s All About The Yarn” for further steps in purchasing a substitute yarn).
Calculating Yarn Requirements For A Substitute
The amount of yarn in meters/yards, not grams/ounces is key to choosing the substitute. Vintage patterns from the 1930s to the 1960s noted how many grams/ounces of yarn were needed to complete a project. This is not an accurate way to determine the amount to purchase. In those days, this made sense since there wasn’t the variety in yarn that we have today. To calculate the substitute amount, say a size small sweater requires 15, 50 gram balls (100 meters each) of double knitting (DK) yarn. DK is a common weight of yarn; there are lots of DK brands available. It’s a simple math calculation: multiply 15 balls by 100 meters (the amount in one ball) which equals 1500 meters, the total amount required. The DK you are interested in has 110 meters per ball; divide 1500 by 110 which equals 13.6. Round up to 14; purchase 14 balls of the substitute. You may want to purchase an extra ball or two so you don’t run out.
Calculating Yarn Requirements If Designing Your Project
Fear of running out of yarn is a big deal when designing your own projects. Estimating generously is a designer’s best friend. Deciding on the amount of yarn is still a best guess, but can be an educated guess.
There are a few ways of calculating yarn requirements. I’ve seen charts that provide quantity estimates for garments at different sizes and gauges, but most are based on classic garment shapes and basic stitch patterns, like stockinette stitch. These amounts do not apply to complex stitch patterns that require more yarn or the different garment shapes.
Another approach is to use the amount specified for a similar pattern that is structured of the same type of yarn and stitch pattern. This may prove difficult trying to find a similar design, and is not precise.
If you can’t find the same type of pattern, although very generous, the following calculation is a better estimate. As a basis for comparison, I have done the calculation for a tank top for which I know the amount used. The calculations below are more accurate for garments without much shaping; you will be buying more yarn than is necessary. My tank has a deep V-neck in the front and back, so the tank from the armhole to the shoulder requires little yarn. I used 5 balls for the tank pictured above.
- Note the number of yards(meters) that are in the full ball of the yarn you want to use. There are professional yarn counters to help if this information is not available. Knit your test swatch from the full ball, then count number of yards (I’m calculating using imperial measurements) remaining, using a tape measure or yarn counter. Subtract the number of yards remaining from the total ball amount to obtain the amount used for the swatch. Full ball for tank equals 104 yds. For my swatch the amount remaining was 50 yds, so 104 – 50 = 54 yds to make the test swatch. The swatch was in stockinette stitch and 5mm needles; not much yarn needed to knit swatch.
- Calculate the area of the swatch. The test swatch measures 6.75 inches wide by 4.25 inches long. Area is 6.75 x 4.25 = 28.7 square inches.
- Calculate the area of the project. Use the schematic as a reference; multiply the widest part of each piece by the total length, equaling the number of square inches per piece. Err on the side of caution; pretend each piece is a rectangle defined by its largest width and length dimensions. Area of tank is 16.5in (widest part) x 21in (length) = 346.5 sqin per piece(x 2) = 693 sqin (total area of tank). The front and back are about the same size. If you have many pieces, like in a sweater, repeat the above process for each piece, then add together the area of each piece for the total area.
- Now you need the number swatches required for the project. Tank’s area 693 sqin (area of project) divided by 28.7 (area of swatch) = 24.1 swatches.
- The number of yards for total number of swatches; 24.1 (number of swatches required) x 54 yards (amount used for test swatch = 1301.4 or 1301 yards.
- Calculate the number of balls needed for the project. 1301 (yardage required for the tank) divided by 104 (the amount in a full ball) = 12.5 rounded to 13. You can purchase 13 balls, or do a further calculation by adjusting for any shaping. Deduct 10% from the total yardage taking into account the V-neck shaping in the tank; 1301 – 10% = 1171 yds. 1171 divided by 104 = 11 balls. This amount is still overly generous at 11, since I actually used 5 balls for the tank. This is the best estimate to calculate the amount of yarn required, without the fear of running out.
After knitting many garments, you will be better able to figure out yarn requirements. This is the best guideline for calculating amounts, and is on the generous side. Better safe than sorry!