Pretty much, though you have to take a couple things into consideration. If there's a repeating stitch pattern, you need to add stitches in increments of the repeats inside the edge stitches. You can sometimes increase a little with larger needles, or if you use really large needles and doubled yarn that can work. Or you can do a combination.
Figure out the sts per inch with the yarn and needles you want to use, then multiply the sts per inch times the width you want, then adjust the number if you need it to fit a stitch pattern repeat.