The true measurement that I use is the measurement of the beads only. I don't include the clasp in the measurement. If the piece is adjustable the lengths will be noted.

Bracelets are typically adjustable or one size fits all

Earrings are measured from the fitting (the piece that goes into your ear)

Sizes of beads can be tricky because not all of the beads are perfectly round. For example 7mm is about the size of a pea and 18 mm is about the size of a penny.