Cost & weight

How much does a piece weigh in each metal?

A plain flat band in UK ring size N½, 4 mm wide and 1.5 mm thick, weighs 3.67 g in sterling silver 925. The same band is 5.52 g in 18ct yellow gold, 6.03 g in 21ct yellow gold and 7.59 g in platinum 950, because the volume is fixed and only the density changes.

Multiply the volume of the piece by the density of the alloy. A shape has a fixed volume, so the only thing that changes between metals is density. A ring that weighs 5 g in sterling silver weighs about 7.5 g in 18ct yellow gold and 10.3 g in platinum, because platinum is roughly twice as dense as silver.

weight (g) = volume (cm³) × density (g/cm³)

Those figures are for a flat section. A D-shape band of the same size, width and thickness holds about 86 per cent of that metal and a court about 79 per cent, because the section is rounded away on one face or both.

Converting a wax model to metal

Weigh the wax, divide by the density of the wax, then multiply by the density of the metal. Carving and injection wax sit around 0.95 to 0.97 g/cm³, so one gram of wax becomes roughly 16.5 grams of 18ct gold or about 22.5 grams of platinum. Casters usually add 1 to 2 per cent, and the sprues and button are extra again.

Wax to metal multipliers

Converting between two metals

The same sum with a different starting density. Weigh the piece in the metal you have, divide by that density, then multiply by the density of the metal you want. Casting a silver master in 18ct gold multiplies the weight by about 1.5.

What this calculator does not include

• Sprues and the button. You pour more metal than you keep, and how much depends on how the tree is built.
• Finishing loss. Filing, emerying and polishing take weight back off, so a finished piece is lighter than the casting.
• Plating. Gold plating is charged by the job. A 2.5 micron layer on a ring is a pound or two of gold, so what you pay is the plater's minimum charge, not the metal.
• Labour, stones, findings and hallmarking.

Why your rate is not the spot price

Spot is quoted for pure metal per troy ounce. Divide by 31.1035 for grams, then multiply by the fineness, so 18ct gold contains 750 parts per thousand of it. Your supplier adds a fabrication charge on top for turning that into sheet, wire or casting grain. On silver that charge is a large proportion of the price, because the metal itself is cheap.

Common questions

How much does a silver ring weigh?

A plain sterling silver band in UK size N½, 4 mm wide and 1.5 mm thick, weighs 3.67 grams. Weight rises quickly with width and thickness, so the same size at 6 mm wide and 2 mm thick is about 7.5 grams.

How do I work out the gold weight from a wax?

Divide the wax weight by 0.95, then multiply by the density of the gold. For 18ct yellow that is 15.58, so a 0.5 g wax casts at roughly 8.2 g before sprues.

Is gold plating worth costing separately?

The gold in a plated layer is worth very little, usually a pound or two on a ring. Price plating as a service charge from your plater, including any batch minimum, rather than as a metal cost.

Which is heavier, platinum or gold?

Platinum at 21.40 g/cm³ is denser than 18ct gold at 15.58, so the same piece is around 37 per cent heavier in platinum. It is denser than 22ct gold too: 22ct is 17.80, so the same piece is about a fifth heavier again in platinum.

Do these numbers include the stone?

No. The calculator prices metal only. Add stone weights and setting costs separately.