Lace weight yarn size is usually knitted with larger needles in order to get an openwork where the stitches are open enough to let the light through. This is the beauty of lace knitting.

Usual gauge: 33 to 40 stitches = 10 cm / 4 inches in jersey.
Recommended needle size: 1.5 to 2.25 mm (#US 000 to 1)
Usual quantity of meters per 100g = 525 to 1200 meters and +.
WPI* (wraps per inch)*= 30 and +

Fingering weight yarn is most frequently used to knit contemporary shawls and socks. If you are looking for a sock yarn, pick one with a nylon blend since fingering wool has the drawback of its quality: being thin enough to be worn in a shoe, it will pierce more easily (hence the usefulness of nylon)

Usual gauge: 27 to 32 stitches = 10 cm / 4 inches in jersey.
Recommended needle size: 2.25 to 3.25 mm (#US 1 to 3)
Usual quantity of meters per 100 grams= 360 to 480 meters
WPI* (wraps per inch)* = 24 to 30

Sport yarn weight is often found in baby knitting patterns but is not only limited to that: it can be used for all purposes

Usual gauge: 23 to 26 stitches = 10 cm / 4 inches in jersey
Recommended needle size: 3.25 to 3.75 mm (#US 3 to 5)
Usual quantity of meters per 100 grams= 260 to 360 meters
WPI* (wraps per inch)* = 18 to 24

Dk yarn weight, also known as "light worsted" weight, is a yarn weight often preferred to knit sweaters. It is not too fine to knit a sweater (those who have ever knitted a garment in fingering weight know what I'm talking about!!) but it is not too thick either so it produces a light knitted fabric that is comfortable to wear in all seasons. Some people will use it to knit thick and warm stockings to wear indoors or thick shawls to wear during winter!

Usual gauge: 21 to 24 stitches = 10 cm / 4 inches in stockinette stitch
Recommended needle size: 3.75 to 4 mm (#US 5 to 7)
Usual quantity of meters per 100 grams= 200 to 290 meters
WPI* (wraps per inch)* = 12 to 18

Worsted yarn weight is a "all-purpose" yarn and is used for all types of projects but especially for clothing and accessories such as hats, mittens and scarves.

Usual gauge: 16 to 20 stitches = 10 cm / 4 inches in jersey.
Recommended needle size: 4.5 to 5.5 mm (#US 7 to 9)
Usual quantity of meters per 100 grams = 180 to 240 metres
WPI* (wraps per inch)* = 10 to 12

Bulky weight yarn has the merit of being knitted very quickly and produces a very thick fabric. Handy for knitting a tick and warm quick project! Bulky yarn is mainly used for knitting thick clothing or accessories such as hats and cowl. It is also popular to work decorative home accessories such as cushions and throws...

Usual sample: 12 to 15 stitches = 10 cm / 4 inches in jersey.
Recommended needle size: 5.5 to 8 mm (#US 9 to 11)
Usual quantity of meters per bale of 100 grams = 120 to 160 metres
WPI* (wraps per inch)*= 7 to 8

Super bulky yarn weight, as its name suggests, is the thicker version of the bulky weight yarn. It is used for the same type of projects as bulky yarn accessories and decorative objects. This said, it is less popular for knitting sweaters since it produces a very thick garment that is not necessarily flattering for all silhouettes.

Usual sample: 7 to 11 stitches = 10 cm / 4 inches in jersey.
Recommended needle size: 8 to 12.75 mm (#US 11 to 17)
Usual quantity of meters per 100 grams = 80 to 140 meters
WPI* (wraps per inch)* = 6 to 7

Jumbo yarn weight is a giant yarn or "roving" (i.e. a ribbon of unspun wool) that is knitted with tree branches with very large needles of 12.75 mm and larger. Many will knit jumbo yarn weight with their fingers or even with their arms. Over the last few years we have seen several videos on the subjectall over the web. The thickness of this yarns implies that there is not much yardage in a 100g ball so you will need a lot of yarn to complete a project, which will be very very thick...

Usual sample: 6 stitches and less = 10 cm / 4 inches in jersey
Recommended needle size: 12.75 mm and larger (#US 18 and larger)
Usual quantity of meters per 100 grams = 80 metres and under
WPI* (wraps per inch)* = 6 and under

The gauge listed in the chart is measured over 10 cm (or 4 inches). If the yarn label gives you the suggested gauge on 1 inch (2.5 cm), simply multiply by 4 to get the 10 cm measurement.

In the example shown here, we see a sample knitted with DK PURE yarn. We can see that 11 stitches are contained in 5 cm (2 inches), which gives us a gauge of 22 stitches per 10 cm.

This gauge corresponds perfectly to the size of DK weight yarn.

WPI or "wraps per inch" is a way of measuring the yarn weight by calculating the number of times you can wrap the yarn over 1 inch (2.5 cm).

This measurement can help you to figure out the yarn weight if its label was lost. To measure the WPI of your yarn, start by winding your yarn around a ruler. The yarn should fit snugly: no overlapping or large gaps between the strands. Do not pull the yarn too hard to avoid falsifying the measurement. If you are unsure of your tension, practice with a yarn of which you know the weight.