Very simple square coaster is only used single crochet and chain.
Putting fabric on wrong side make coaster much nicer.
You can download PDF file here：Single Crochet Square Coaster
3.50mm crochet hook
Fabric for lining(desired)
sc = single crochet
sc2tog = single crochet 2times together
sl st = slip stitch
Row1: ch26, sc2tog in 2nd and 3rd ch from hook, ch1, [sc2tog in next 2ch, ch1] repeat across, 1sc in last ch. Turn.
Row2: ch1(do not count as sc), 1sc in sc below, skip next ch1 sp, [ch1, 1sc in next sc, skip next ch1 sp] repeat across. Turn.
Row3: ch1(do not count as sc), [sc2tog in next sc and ch1 sp, ch1] repeat across, 1sc in last sc of row below. Turn.
Row4-23: repeat row2 and row3.
Fasten off. Weave in ends.