How do you knit an elastic rib stitch?

The most elastic of the rib stitch combinations is k1, p1, followed by k2, p2. Once you get beyond that you do not get the same amount of draw in or stretch. Other combinations, Quaker Rib, Fisherman's Rib, and such, are more decorative than stretchy and elastic.

Yes, rib stitch or ribbing (a stretchy knitting stitch often used on cuffs and collars) is a combination of knit & purl. 1x1 rib is knit one stitch, purl one stitch (repeat to end). 2x2 rib is knit two stitches, purl two stitches, etc. 3x1 rib is knit three stitches, purl one stitch. There are lots of combinations. For ribbing, you "knit the knits and purl the purls." If you do the opposite, you'll knit seed stitch instead of rib. (The pattern directions depend on whether you have an odd or even number of stitches and whether you are knitting flat or in the round.) Here's a good explanation: http://www.thedietdiary.com/blog/index.php?p=261

depends on the width of the ribbing. usually k2, p2, or k1, p1. good luck with your dress:)

http://www.ehow.com/how_2062551_knit-rib-stitch.html

in knitting a rib, everyone whos answered is correct in that it is a combination of knitting & purling. But you need to remember 1 key thing or you're going to end up with a seed stitch instead. When you are finished with your row, and turn your work, any stitch that was knit now needs to be purled, and vice versa. i.e. Row 1: K1, P1, K1, P1 Row 2: P1, K1, P1, K1

The elastic rib stitch is the k1p1 or a variation of that. There are rib stitches that aren't elastic, usually involving slip stitches to make the "rib". If you want the the stuff to stretch less, use twisted stitches for the purl/background stitches. Will you be knitting up or knitting down? Accordingly, the cast-on or bind-off method must be suitable for your garment's bottom edge. If you're not certain, do samples first to confirm elasticity and recovery and over-all appearance.