In order to have any knitting, crochet or machine knit FIT the desired size, it is necessary to make a SWATCH with your desired yarn.
Treat the swatch as you would the finished item………….. i.e. wash and dry in your chosen method or at least as suggested on the Yarn Ball band.
MEASURE the swatch and consider the results. How does it feel? Is it loose or too tight? Repeat the swatch, making the needed adjustments. Write down your findings and the needle/dial numbers.
The SECRET to making things fit is #X number of stitches per inch/cm.
and #Y number of rows to the inch/cm. This is known as the gauge.
Multiply the measurements that you need for your item, by the gauge information.
For Example: If, the gauge is 4 stitches/inch and you want 10 inches, The answer is 40 stitches.
Yarns will have different characteristics, as will colors due to the dyes.
Knitters produce different gauges, due to personal handling of the needles; tightly or loose. Knitting machine carriages will also knit differently from one to another, including same brand and model.