Yarn weight gets you in the right range, but gauge is what decides how your piece fits. 

Sport weight usually knits at: 23-26 stitches over 4 inches on US 3 to 5 (3.25 to 3.75mm) knitting needles and crochet hooks. 

It sits between fingering and DK, so it knits up faster than fingering but stays light enough to wear most of the year. Knit a swatch and block it before you measure, even if the label matches your pattern. Sport yarn is ideal for lightweight sweaters, cardigans, baby knits, hats, mittens, and colorwork that you want to finish faster than fingering.