If you are unsure of your nail measurements you purchase a sizing kit prior to ordering. 

This kit contains 10 nails, one for each size.

Shape of nails in this kit will be random.

Once you have sized your nails, you can determine whether you fit a predetermined nail size (XS, S, M, L). If your nails do not fit a predetermined size, simply select the "Custom" option in the size drop box.  At checkout, enter your nail sizes in the "Special Instructions for Seller" section.