The phrase "appropriate size" means choosing something that is just right for a particular purpose or situation. It implies selecting something that fits well or is suitable for the task at hand. Full definition
Be sure to buy toys of appropriate size for your dog. (humanesociety.org)
Transfer the layer to a table and immediately cut round 18 cm / 7 in in diameter using a large baking circle (or a plate of appropriate size as a guide). (bake-no-fake.com)
You can also use pot lids in appropriate sizes as long as the lids have sharp, well - defined edges. (glutenfreeonashoestring.com)