I brought this pattern then realised it was a USA, the pattern is worsted yarn #4, size 7 needles. I dont have any worsted yarn bit lots of DK, would DK be OK to use and what size needles. The pattern is a car seat blanket.
What’s the name of your pattern and/or designer?
DK is a bit lighter than worsted, so the blanket would come out a bit smaller. I’d do a swatch with the needle size your yarn band suggests, and then calculate the new dimensions to see if it would be large enough, or if you need to cast on more stitches.
You might also try your DK yarn with 4.5 mm needles and see if you like the fabric and if the gauge comes out closer to that of the pattern.
As yarns within a weight name are a range of thicknesses you might have a thicker DK you can try. I have a DK which i prefer on 5mm needles because it’s quite firm on 4mm whereas another DK is much finer and feels good on 4mm.
I’ve also been purposely using finer weight yarn with patterns for heavier weight yarn, on the needle size for the pattern which gives a softer fabric. You mght not want a softer fabric for a car blanket but it’s worth experimenting with a swatch or even several.
You might also try a fingering or lace weight held together with your DK on the 4.5 mm and see how you like that.