For example: 18-inch princess necklace made with 4mm beads: 18 x 25.4 ÷ 4 = 114.3. 32-inch opera necklace made with 10mm beads: 32 x 25.4 ÷ 10 = 81.2.
Necklace?
Type Length
Collar 14 to 17 inches
Choker 16 to 18 inches
Princess 17 to 19 inches
Matinee 20 to 25 inches