For a 15" x 15",  Ch 90
Multiples of 6,
W/ baby yarn, 6 sc is 1 inch, w/ F hook.
 
1.Chain 90,
2.Sc in 3rd chain from the hook.
*ch2, sk2, sc in next*, to end of row.
ch 1, turn
3.SC first sc, *ch2, sk2, sc in next*.
last stitch of the round is in the first sc of the previous round,
ch1 turn.
repeat round 3 till you have the length that you want.