Press-on sets fail on fit far more often than on design. A set with eight sizes forces most people to file a tip down or wear one that overhangs, and an overhanging tip lifts at the corner within a day. Measuring takes two minutes and removes the whole problem.
How to measure
Tear a strip of paper about a centimetre wide. Lay it across the widest part of your nail — usually just above the cuticle, not at the tip — and mark both edges with a pen. Measure between the marks with a ruler in millimetres. That number is your size for that nail.
Measure every nail, including both thumbs
Hands are not symmetrical. Most people are one size different between the left and right index finger, and the thumb is usually two to three sizes above everything else. A set sized from a single measurement will have two badly fitting nails, and those two will be the ones that lift.
If you are between sizes
Take the smaller one. A narrow tip sits inside the nail edges and looks like a natural nail. A wide tip sits on skin, where adhesive does not bond and oil is constantly present — that is the tip that pops off in a day and takes the neighbours with it.
Why fifteen sizes, not eight
Eight sizes covers the middle of the distribution. Fifteen covers the tails: the very narrow little fingers and the wide thumbs, which is where most fit complaints come from. It costs more tooling and more packaging, and it is the only part of this category that reliably reduces complaints.
Shape and length, briefly
Almond tapers to a rounded tip and is the most forgiving on short nail beds. Square has straight sides and a flat edge and is the most durable. Coffin tapers to a flat tip and gives the longest look. Squoval is square with softened corners, the easiest to wear at a desk. Length is measured on the finished tip, cuticle to tip, not on your own nail.
The full size table, including the millimetre width of all fifteen sizes, is on the size guide. Every press-on set ships with 30 tips across those 15 sizes, two per size.