How to find a ring's metal weight from its 3D file

The idea in one line

A piece of metal weighs its volume times its density. A ring's 3D file already holds the volume, so the only things left to decide are which alloy you will cast and which parts of the model are not metal. The metal density entry explains why the same ring weighs more in platinum than in 14k gold.

Step 1: Check the units

Every weight starts from the size of the model. A Rhino 3DM file stores the unit it was drawn in, so its size is known. An STL file stores bare numbers with no unit, so a ring drawn in millimetres can be read as centimetres or inches. Before trusting a weight, check that the reported size of the ring looks right: a ring band is about the width of a finger, not the width of a room.

Step 2: Keep the stones out

The metal's volume should not include the diamonds and gems. In a well-built model each stone is its own object, so it can be left out of the metal and counted on its own, with its carat weight. If the stones are merged into the same mesh as the metal, the volume includes them and the weight comes out too high.

Step 3: Multiply by the alloy's density

With the metal's volume known, the weight in any alloy is one multiplication. The alloy density table lists the density of every common casting alloy with the supplier it comes from, so the figure you use is the one your caster works with.

Do all three in your browser

The free metal weight calculator does these steps for you. Drop a 3DM, STL, GLB or OBJ file, and it measures the metal's volume, keeps separate stone objects out and lists them with their carats, and shows the weight in every common gold, silver and platinum alloy at once. The file stays in your browser.

From weight to price

The weight from a 3D file is the CAD weight: the model as drawn, before any metal is lost in casting and finishing. To turn it into a price, add your casting loss allowance and your own price per gram. The free ring cost estimator takes the weight and your rates and shows the metal you pay for. Inside the studio, the weight and cost guide explains how the same measurement prices every ring a shopper builds.