Method
How Culet Studio measures
Every number in the report comes from your model's geometry and a published formula. Here they all are, with the limits, so you can check our working.
Labels
Measured, estimated or inferred
The report marks every value that isn't a straight measurement of the geometry:
| Label | Means |
|---|---|
| (none) | Measured from the model's geometry |
| est. | Calculated from the geometry and a reference value, such as an alloy density or a stone's specific gravity |
| approx. | Measured, but the model makes it uncertain, for example an open mesh or a size scale keyed on approximate trade charts |
| inferred | Worked out because the file doesn't say, for example the units of an STL |
Ring size
Ring size from the bore
Culet Studio works on any piece of jewelry. This section applies when the piece is a ring; for pendants, earrings and other pieces the report shows the overall dimensions instead.
The studio finds the finger hole and fits a circle to it. That gives the inner diameter (ID). Everything else follows from it:
| Scale | Formula | Notes |
|---|---|---|
| Inner circumference | π × ID | |
| US / Canada | (ID − 11.63) ÷ 0.8128, to the nearest ¼ size | So US 7 = 17.32 mm |
| ISO / EU | Inner circumference in mm, rounded | ISO 8653 sizes by inner circumference |
| UK / AU | Letter from the circumference, in half sizes | Marked approx.: trade charts differ |
| India | Circumference − 40 | Marked approx.: trade charts differ |
The report also gives band width and thickness at 6 o'clock and at the shoulders, the inside profile (flat or comfort fit) and the head height above the finger. If the file stores no units, the studio picks the unit that makes the finger hole a real ring size and tells you which one it chose.
Metal weight
Weight in every alloy
weight (g) = metal volume (mm³) ÷ 1,000 × density (g/cm³)
The volume is the closed metal solid only: stones, cutters, sprues, tie bars and order-number text are left out, and overlapping parts are counted once. One volume gives the weight in every alloy:
| Alloy | Density used (g/cm³) |
|---|---|
| 14K yellow gold | 13.07 |
| 14K white gold | 12.61 |
| 14K rose gold | 13.26 |
| 18K yellow gold | 15.58 |
| 18K white gold | 14.64 |
| 18K rose gold | 15.18 |
| 22K yellow gold | 17.88 |
| Platinum 950 | 20.10 |
| Palladium 950 | 12.00 |
| Sterling silver 925 | 10.36 |
These are typical trade values. Alloy recipes vary between refiners, so use your caster's own figure when you have it. For the full method and the mistakes that make CAD weights wrong, read how to calculate gold weight from a CAD file.
Stones
Stones and carat estimates
Stones are found by their shape, not by layer names, and given a role (center, halo, side or shank) from how they are arranged. Each one gets its shape, length × width × depth and an estimated carat:
carat = stone volume (mm³) × 3.52 ÷ 200
3.52 g/cm³ is the specific gravity of diamond, and 1 ct = 200 mg. Colored stones have their own specific gravity, so their carats differ from this figure.
Casting checks
Every check and its threshold
Checks about the size, the band, the sizing area and the culet's clearance to the finger run on rings. Every other check runs on any piece.
| Check | What it looks at | When it flags |
|---|---|---|
| Watertight solid | Counts open (naked) edges in the metal | Any open edge: warning. The weight becomes approximate |
| Open surface patches | Finds metal surfaces that were never joined into solids | Any: warning |
| Loose fragments | Separate metal bodies smaller than 0.5 % of the metal volume | Any: warning |
| Overlapping solids | Metal bodies that overlap, such as claws sunk into the shank | Counted once in the weight: note |
| Production helpers | Sprues, tie bars, template rods and order-number text in the finger hole | Left out of the weight and measurements: note |
| Size against the file name | Compares the measured US size with a size in the file name | More than ¼ size apart: warning |
| Shank thickness | Band thickness at 6 o'clock | Under 0.5 mm: fail |
| Wide band | Band width at 6 o'clock | Over 4 mm: note (often needs +½ to +1 size for comfort) |
| Sizing area | Stones within the 60° arc centered on 6 o'clock | Any stone: warning (the ring can't be resized there) |
| Stones through the bore | A culet or pavilion poking inside the inner surface | Any: fail |
| Center culet clearance | Gap between the center stone's culet and the inner surface | Below the surface: fail |
| Claw width | Narrowest claw, measured at the girdle | Under 0.5 mm: fail. 0.7 mm or less under a center of 1 ct or more: warning |
| Stone gaps | Smallest girdle-to-girdle gap between stones | Under 0.08 mm: warning (usual pavé is about 0.08–0.25 mm) |
| Intersecting girdles | Stones that pass through each other | Any: fail (they can't both be set) |
| Center-stone proportions | Table, crown and pavilion of a round brilliant | Compared with table 52–62 %, crown 32–36°, pavilion 40.6–41.8° |
Limits
What the numbers can't tell you
- Carats are estimates from the modeled stone. CAD stones are often idealized; the real stone will differ.
- The weight is the model's. The cast copy adds sprue and claw allowances and loses metal in finishing. Ask your caster for their allowances.
- Open meshes give approximate volumes. Repair the model before you rely on its weight.
- UK and India sizes are approximate: trade charts don't agree with each other.
- It doesn't edit CAD or grade stones. Fix models in your CAD software, and grade real stones with a lab.
- It isn't a substitute for your caster's and setter's checks. It helps you find problems earlier.
See every detail before it's cast.
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