To size your nails at home, measure the widest horizontal point on your nail plate. Choose the size closest to your measurements.
The following is a list of nail sizes from thumb to pinky.
SMALL:15mm, 11mm, 12mm, 11mm, 8mm (2,6,5,6,9)
MEDIUM: 16mm, 12mm, 13mm, 12mm, 9mm (1,5,4,5,8)
LARGE: 18mm, 13mm, 14mm, 13mm, 10mm (0,4,3,4,7)