About to buy some yarn? Read this first! We'll explain why a yarn's weight has nothing to do with grams or kilos, reveal what is meant by fingering, sport and worsted weight yarn, and help you choose the right yarn for your project with our yarn weight conversion chart.
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What is yarn weight?
When choosing the right yarn for your project, size matters. Knitting yarns come in a wide range of different thicknesses, or 'weights', and the weight of yarn you choose will have a big impact on the look and feel of your finished fabric. To get the best results it's a good idea to use the weight of yarn specified in your pattern, although tools such as YarnSub can help if you want to find a substitute. Take care not to mix different weights of yarn in one project, unless it's a novelty look you're after!
As a yarn's weight is determined by its thickness, a thin yarn such as lace is described as 'light', while a thick yarn such as super-chunky is 'heavy' – regardless of the overall weight of the ball. Yarns come in a range of standard sizes (the most well-known being set by the Craft Yarn Council), which can be found written on the ball band along with the suggested needle size and tension. You can find our guide to these weights below.
What does ply mean?
Ply refers to the number of strands that are plied, or twisted together, during spinning to create a single strand of yarn. A 2ply yarn has two strands, a 3ply has three and so on. If you've ever untwisted or split your yarn while knitting, you'll have seen these individual plies.
Historically, yarn weights were named after these numbers, so the higher the ply the heavier the yarn, but today it's more complex than that. A 4ply yarn might not have four plies – it could have more or fewer. And a singles (1ply) yarn could be lace weight, big or somewhere in between. Plies are still commonly used as names for yarn weights, particularly in the UK and Australia, even though weight and ply are no longer always related!
What yarn weights are there?
Here are the yarn weights you'll most commonly encounter in the UK, and our recommendations for what to knit with them. Use our yarn weight conversion chart to help translate these to US terms.
1, 2 and 3ply
Knit on 2 to 3½mm needles. Use for delicate lace knitting and baby garments. Good for socks and gloves.
4ply
Knit on 3 to 4mm needles. Great for baby clothes, heavier socks and lightweight tops.
Double knitting (DK)
Knit on 3½ to 4½mm needles. Usually double the weight of 4ply, this is the most widely used weight. Suitable for most garments and quick to knit up.
Aran
Knit on 4 to 5½mm needles. Originally created for fishermen’s jumpers. Use when DK isn’t heavy enough, and chunky is too bulky. Perfect for outdoor or warm clothing.
Chunky
Knit on 5½ to 7mm needles. Associated with outdoor wear and winter jumpers, great for oversized garments.
Super chunky
Knit on 7 to 12mm needles. A great weight for beginners, as it produces quick results. Good for furnishings.
Big
Knit on 9 to 20mm needles. Perfect for eye-catching scarves and coats, as well as cosy cushions and throws.
Or print out and keep our handy yarn weights chart:
What is fingering weight yarn?
The yarn that UK knitters will be familiar with as '4ply' usually goes by the name 'fingering' in the US. You might also see it referred to as 'sock' or 'baby' weight because – you guessed it! – it's an ideal weight for socks and baby garments. It's generally knitted on size 3-4mm needles and is a popular choice for lace shawls as it knits up into a light but cosy fabric.
What is sport weight yarn?
If you're looking at US yarn brands or patterns, you might see sport weight yarn mentioned. There's no direct equivalent in the UK as sport weight sits between two categories: heavier than 4ply but lighter than DK. As a result you can generally use it as a substitute for both weights, but make sure you swatch, swatch, swatch first with knitting tension squares to check that your tension is a good match!
What is worsted weight yarn?
This popular yarn weight (it's reportedly the most-used yarn in the US) is equivalent to UK aran. Worsted weight yarns are medium thickness and knit up on 4-5½mm needles, making them a good choice for beginners and winter knits such as jumpers and blankets. Light worsted is the same as DK in the UK.
Note that the term 'worsted' can also refer to the way the yarn is processed – it can either be worsted spun or woolen spun – so you may see it used in the context of yarn manufacturing and spinning as well.
Yarn weight conversion chart
Yarns come in a standard range of sizes, but the names can vary from country to country. Here's our at-a-glance guide to the most common yarn weights in the UK and US, and the needles to use with them:
UK
US
Needle size
4ply
Fingering/Sport
3-4mm
Double knitting
Light worsted
3½-4½mm
Aran
Fisherman/Worsted
4-5½mm
Chunky
Bulky
5½-7mm
Super chunky
Extra bulky
7-12mm
Or print out and keep our handy yarn weight chart:
How to convert knitting patterns if you have a different yarn weight
There are various reasons why you might not want to knit a pattern in the suggested yarn. Perhaps it’s a fibre you find uncomfortable, or maybe the pattern is old and the original yarn has been discontinued. Or perhaps you simply want to spice up the design by making a change, or use yarn you already have in your stash rather than buying new meterials.There are several things to consider when substituting yarns – and a little bit of maths! The easiest substitution is ‘like for like’, where you swap in a similar weight yarn, though you might need to do some sums to work out the amount of new yarn you require if it’s sold in different lengths.
For more significant changes it’s best to experiment with plenty of tension squares and to consider the finished effect – details such as cabling won’t show up with a fluffy yarn, for instance. But you can work out how to convert a knitting patten to a different yarn weight by knitting tension squares.If you don’t have the same tension as the pattern, you will not be able to reach the stated pattern dimensions by following the printed instructions.First you must knit your new swatch in the yarn or to the tension you want to work with. This will be the fabric your project is made from, and must be large enough to accurately measure your new tension from. The standard size for a swatch is 10cm x 10cm (4in x 4in), but if your project uses a complex motif or texture, make sure your swatch contains at least one pattern repeat, plus enough extra on all sides that the motif isn’t distorted at the edges. Be sure to wash your swatch in the same way you will wash your final project, and let it dry before taking measurements.
To get the new stitch counts, we need to divide the old stitch count by the old tension, then multiply it by the new tension for every single row. The pattern schematic helps us see the main measurements of the garment that have to stay the same regardless of tension.
Here's the pattern schematic for our knit crop top pattern. Checking the width at different parts of the design lets you check measurements are what you expected them to be even after you have converted your yarn weight.
Check the width of your garment at particular points to confirm that it matches what you would expect to see with the pattern schematics It's really helpful to see instructions like “continue until work measures x cm” in your original pattern. As that’s a fixed measurement, we can use that as guide for our new yarn weight, too
More knitting advice
If you're new to knitting, patterns can look like they're written in another language. But don't worry, we're here to translate! Whether you're on your first project or just need a quick refresher, check out our knitting abbreviations for the common stitches you'll find in our patterns. From 'alt' to 'yo', it's all there. Now that you've mastered yarn conversions find a project to work on with our knitting patterns collection, and see our guides to the best knitting kits for beginners and knitting books for more inspiration.
