Shapes

If you have very flat nail beds, the best shapes would be
Short Oval, Short Square, Medium Round and Medium Almond.

Short press-on nail shapes
Medium round and sqaure press-on nail shapes
Stiletto, almond and coffin medium press-on nail shapes
long coffin and stiletto press-on nail shapes

Sizing

chart showing press on nail sizes
Step One

Place a clear piece of tape over your nail.

Step Two

Using a marker, mark the outer edges of your nail.

Step Three

Remove the tape from your nail and place it on a measuring tape.  Measurements must be in Millimeter and not converted from Inches.

If you have very flat nail beds, the best shapes would be Short Oval, Short Square, Medium Round and Medium Almond.