The Standard Yarn Weight System classifies DK yarn as a  Light Weight. DK weight is thinner than Worsted  Medium and thicker than Sport  Fine.
(:1f9f6:) What size needles for DK yarn?
On average needles US 5-7 (3.75 to 4.5mm) are used.
(:1f9f6:) Is worsted weight yarn the same as DK?
Worsted weight yarn is slightly thicker and uses US Needles 7-8. Dk Weight is thinner and uses US 5-7 (3.75 to 4.5mm) needles. Worsted works up to 4 to 5 sts per inch. DK works up to 5.25 to 6 sts per inch.
(:1f9f6:) What is DK weight yarn used for?
This medium light yarn is often used for children's garments and lighter weight garments for spring or fall weather.