The traditional 5-ply Guernsey yarn was named for the Channel Islands but was spun from local wool in coastal areas all around the UK and Northern Europe. It was then knitted into warm working wear for sea-faring and (we have no doubt) farming and mining people. Also of course we get 'Gansey' and 'Jersey' from the same creative roots.
The 5-ply construction makes a yarn which locks together well to make a garment wind-proof. The worsted spinning creates a crisp and lean yarn with excellent stitch definition for fancy textured designs but also helps soften the handle of the local wool whatever breed it is from. The yarn is supplied in 50g balls, as described on the Details tab on each individual product page. Linking land and sea, the natural colours are dark peat, foamy cream and pewter, along with rich dyed shades to reflect sea, shore and rocks.
Normally each 50 gram ball of Guernsey yarn will be around 116 metres (121 yards) long, but this varies from breed to breed, so to be on the safe side you should work on plus or minus 10%. See our information sheets and download the one on ball yardages and remember that this densely twisted worsted spun yarn is not elastic so will go less far than a woollen spun yarn, and it's worth getting a couple of balls extra for a pullover project, to be on the safe side and match the batch numbers.
TENSION: to be sure of tension, you should always knit a sample tension swatch. Generally the knitter is one variable, but the pattern is another, depending on the intentions of the designer! As a guideline: for our Guernsey, on 2.25mm/US 1, UK 13 needles you will get 30 sts and 40 rows to a 10cm/4" square.
However, you can also work a Guernsey yarn as a 4-ply or DK to make a less dense fabric, but with excellent stitch definition. For example, on 4mm/US 6, UK 8 needles, you will get around 22 sts and 30 rows to a 10cm/4" square. But remember that this yarn is less elastic, so you may need more yarn than stated in a pattern, unless it is specifically for a Guernsey design. The WPI is usually 20 in worsted spun yarns.