Wrap a soft tape measure around the nail piece to measure the widest part of its
curvature. If you don't have a soft tape measure,you can use a piece of paper to wrap
around the nail. After making a mark, use a ruler or a smartphone app store to search
for "ruler" and download a measuring app(unit: millimeters,mm).
Warm tip: It is recommended to choose a size that is slightly larger. If the majority of fingers fit, and only a few fingers are 1mm smaller, then select the nail piece size that matches the majority of fingers.