gauge instructions

[Carol1213]

instructions for gauge: [ch1, sk next st, sc in next st] 8 times = 4 inches

18 rows = 4 inches. How do I begin? 24 chains?

 

[Granny Square]

Ideally you want to crochet a swatch bigger than 4" and measure the center 4" and count those stitches (shh, don't tell anybody, I don't always do that, but it IS a good idea as the edge stitches can sometimes be not representative of the rest).

To answer your question - I wouldn't bother to do the 'stitch repeat math', rather just chain more than 4", say 5 or 6, turn and work back until you have at least 4" across and can't do another repeat, and work up from there.  If you want to keep your swatch, you can pick the extra chains out (it won't unravel from the knot end.)