Wraps per inch method

How to buy enough yarn using the Wraps Per Inch method

Ahhh, you're looking at a fine skein of yarn, and don't yet have a pattern or design. It's on sale, it's calling your name. You've got to buy it. How much to buy? Here is a simple method of determining how many yards of yarn you'll need using the Wraps Per Inch (WPI) method:

wraps per inchWrap your yarn around a pencil, or ruler or any other similar object and count the number of wraps per inch. You can even make a tool with the inch marks indicated on the dowel but a ruler works great too since it's already marked off. If you're worried about pulling apart a skein you haven't purchased yet, just lift up an inch worth of strands away from the skein without disturbing the hold. In this photo I wrapped around a pencil and measured against a ruler. There are 12 wraps over one inch so my WPI is "12".

Wrap somoothly, with the yarn touching but not too tight. When measuring thicker yarns it's best to do the wrapping over several inches and then divide (i.e., wrap over 3 inches and divide by 3). Once you've wrapped, calculate your number of wraps per inch (or WPI)

Refer to this handy chart A (or print and keep in your wallet!). This chart is for an average adult pullover sweater.

You'll notice that the yardage is equal to the WPI X100 (12 wpi for worsted weight X 100 is 1200 yards you'll need to buy). So if you can memorize this formula you can buy yarn anywhere, anytime.

To adjust the yardage for other sizes, add or subtract the % according to chart B

*See this link for determining gauge

Chart A: Yardage using WPI

Type
WPI
*Gauge in stockinette
(stiches per inch)
Needle size
Yardage
med sweater 36-38" plus 2" ease
lace
18+
8+
#00, 1, 2
1800-2200
fingering
16
6-8
#2, 3, 4
1600-1900
sport
14
5-6
#4, 5, 6
1400-1600
worsted
12
4 1/2-5
#7, 8, 9
1200-1400
bulky
10
3 1/2-4
#10, 10 1/2, 11
1000-1200
super bulky
8
2-3
13, 15, 16
800-1000


Chart B: Calculating other sizes

Size chest measurement Add or subtract
Child 25" or less subtract 30%
Ex. Small 28"-30" subtract 20%
Small 32"-34" subtract 10%
Medium follow chart above  
Large 40"-42" add 10%
Extra Lg. 44"-46" add 20%

Keep in mind for other sweater styles you'll need to add or subtract. Here is a guideline:
Add 10% for cable designs or other similar textures
Add 30-50% of total yarn needed for fair isle or other designs requiring a yarn carry to the inside.