My square came out to 6 1/8 inches using worsted weight yarn and an I hook (5.5mm). Different yarns/hooks will produce different sizes. The square doesn’t require much yarn.

This is listed as an afghan block, but it can be used for so much more. Some ideas are…

Ponchos
Scarves
Blankets
Pillows (crochet 8 squares together, 4 in front and 4 in back)
Placemats
Tree skirt?
Totes
Coasters