For the best results it is always recommended to use the yarns specified in the pattern. That way you know what your garment will look like when finished.
For those of you who are aware that using a different yarn will change the look and feel of the item, then substituting yarns is simple.
When substituting yarns I recommend just taking a little time to look at a few things and do a few experiments. The first one is very important, find another yarn that gets the same tension.
This doesn’t mean using the same needles as specified in the pattern but getting the same tension, e.g 18 stitches and 24 rows to 10/4ins square. Then the item will be the same size as mentioned in the pattern.
For the yarn amounts look at the length on a ball band, not the grams.
For example, if the original yarn has 135m per 50g ball and the pattern asks for 3 balls. The maths is 135m multiplied by 3. This equals 405m.
Next look at the length on your substituted yarn, for example 124m per 50g ball, so divide 405m by 124m. This equals 3.3. Which means you need just over 3 balls (i.e 4 balls) to make the garment.
At first it can seem very confusing and a little bit daunting but once you have mastered it and are aware that your finished item will be unique, it is lots of fun!