Measuring and calculating in jewelry: gauge, sizes and metal weight

Almost everything in jewelry is measured. These are the concepts and the sums used most at the bench.

Vocabulary #

• Gauge (calibre): a number that tells the thickness of sheet or wire. The American system (AWG or B&S) is the most used: the higher the number, the thinner the metal. Europe uses millimeters.
• Thickness (espesor): how thick a sheet is.
• Diameter (diámetro): the width of a circle or round wire.
• Radius (radio): half the diameter.
• Circumference (circunferencia): the perimeter of a circle, equal to π × diameter.
• Ring size (talla de anillo): the measurement of the inside of the ring. See how to find your size and mandrels and sizers.
• Weight (peso), density (densidad), volume (volumen): weight is volume multiplied by density.

Gauges and millimeters #

Ring size conversion #

European ISO sizes equal the inside circumference in millimeters. Other countries use their own numbers; always check the chart of whoever makes the ring.

Length of metal for a ring #

Length = π × (inside diameter + metal thickness). For a ring with a 17.3 mm inside diameter made from 2 mm strip: 3.1416 × 19.3 ≈ 60.6 mm.

Weight of a piece #

Weight (g) = volume (cm³) × density (g/cm³).

Example: a round wire 2 mm in diameter and 60 mm long has a volume of π × 1² × 60 ≈ 188 mm³ = 0.188 cm³. In sterling silver it weighs 0.188 × 10.36 ≈ 1.95 g; in 18-karat gold, about 2.9 g.

Alloy percentage #

An 18-karat alloy is 75% gold. To make 100 g you need 75 g of pure gold and 25 g of other metals (copper, silver…). See alloys.

Measuring accurately #

A caliper and a scale reading tenths of a gram are enough to start.