Calibrated vs freesize stones: what it means for jewellery CAD

By Ronak Rawal · 1 October 2026 · 2 min read

Stones come in two broad groups: calibrated and freesize. Which one you use changes how the model is built, and how easy it is to produce the piece again.

Calibrated stones

These are cut to standard sizes, such as 1.5 mm, 2.0 mm or 6.5 mm round. A seat modelled for the size will fit any stone of that size. This is common in production jewellery, where the same design is made repeatedly.

Freesize stones

These are cut to get the most from the rough, so their size varies from stone to stone. A seat modelled for one stone may not fit another. Freesize stones are common in one-off pieces, and in coloured gemstones.

What this means in CAD

• Calibrated: one seat size works for all, and the design is easy to repeat.
• Freesize: the designer needs the exact measurements of the actual stone, and the seat is built for that stone only.

Which to choose

For a collection or repeat orders, calibrated stones save time and reduce errors. For a unique piece with a special stone, freesize is fine, but the model must be made after the stone is chosen. See how stone seats are modelled.

Give the designer the stone details in your brief.