Lapidary Rough Gemstone Yield & Cost Per Carat — Results
Input / Output
Value
Formula: Rough carats = weight × 5 | Facetable ct = rough ct × facetable% | Finished ct = facetable ct × yield% | Cost/ct = rough cost ÷ finished ct. Source: International Gem Society / Jeff R. Graham. Generated:
How to Use This Calculator
Enter rough weight in grams or carats (toggle above). Every gram of rough contains exactly 5 carats.
Set the facetable portion — estimate what percentage of the piece is clean and cuttable after removing fractures, matrix, and inclusions.
Choose a cut type to auto-set a typical yield range, or select "Enter yield manually" and type your own number.
Enter pricing — what you paid for the rough, any labour cost, and the expected sale price per finished carat.
Read results instantly — finished carats, cost per carat, total COGS, revenue, and gross profit update live.
Understanding Yield in Lapidary Work
Every piece of rough gemstone loses weight at two stages. First, the clean-up stage removes fractures, veils, inclusions, and matrix — this is your facetable percentage. Second, the actual cutting reduces the clean rough to a finished stone, which is your cut yield. The combined effect is your overall yield: for a 20 g piece with 85% facetable and 30% cut yield, the overall yield is just 25.5% — meaning you keep about 1 in 4 carats of rough weight as finished stone.
Typical Yield Ranges by Cut Type
Custom faceting (free-cut for yield) — 25 to 33 % of clean rough
Factory / calibrated-size faceting — 15 to 25 % (cutting to a fixed size wastes more)
Cabochon cutting — 40 to 60 % (less crown removed, no facet grinding)
Carving — 50 to 70 % (material removal is controlled by the design)
Very irregular or heavily included rough — as low as 10 to 15 %
The International Gem Society's Jeff R. Graham notes a quick conservative rule: assume 1 finished carat per gram of rough (20% yield) for budgeting; 30% yield is a more typical expectation for hand-select facet-grade material.
Why Cost Per Finished Carat Matters
The purchase price listed on rough is per carat of rough weight — but you'll only cut a fraction of that into saleable stones. A piece priced at $30/ct rough that yields 30% costs you $100/ct finished, before labour. This calculator makes that conversion automatic and adds the profit outlook so you can evaluate any piece of rough before buying or cutting it.
Worked Example
Scenario: You purchase a 20 g piece of tourmaline rough for $150. About 85% is clean and cuttable. You plan custom faceting at a 30% yield. You expect to sell finished stones at $80/ct wholesale.
At $30/ct rough with 30% yield the cost jumps to ~$100/ct finished — still potentially profitable on premium material priced at $180+/ct retail, as Jeff Graham's tourmaline examples demonstrate.
Frequently Asked Questions
What is a typical faceting yield percentage for rough gemstones?
For custom faceting of clean, well-shaped rough, expect 25–33% yield. Factory or calibrated-size cutting typically yields 15–25% because forcing the stone to a fixed calibrated dimension wastes more material. Cabochon cutting yields 40–60% and carving can reach 50–70%. Very irregular or heavily included rough may yield as little as 10–15%. These ranges come from International Gem Society data and Jeff Graham's published lapidary guidelines.
How do I calculate cost per finished carat from rough gemstone?
Divide your total rough purchase cost by the estimated finished carats: Cost per finished carat = Rough cost ÷ Finished carats. Finished carats = (Rough weight in grams × 5) × (facetable %) × (cut yield %). Add labour cost to get your full cost-of-goods per carat. This is exactly the calculation this tool performs live.
How many carats are in a gram of rough gemstone?
Exactly 5 carats per gram — because 1 metric carat = 0.2 grams (the international standard adopted in the US by 1920). So a 10-gram piece of rough contains 50 carats of rough weight. After yield losses from cleaning and cutting, you will recover only a fraction of that as finished stones. Specific gravity of the stone type does not affect this calculation when you have an actual scale weight.
Why does the facetable percentage matter separately from yield?
Not all rough is clean and cuttable. A piece may have fractures running through it, matrix (host rock), inclusions, or badly windowed surfaces that must be removed before the stone can be dopped and placed on a faceting machine. The facetable percentage estimates how much of the total rough weight is actually usable after that clean-up. The yield percentage then applies only to that clean portion — compounding the two losses gives your true overall yield.
Does gemstone type affect the rough-to-carat conversion?
No — specific gravity only matters when estimating carat weight from millimetre dimensions (e.g. for a mounted stone you cannot remove). When you have an actual scale weight in grams, the conversion is always 5 carats per gram regardless of whether it's tourmaline (SG 3.06), sapphire (SG 4.00), or opal (SG ~2.10). The gem type affects how heavy a given volume of finished stone will be, but not the gram-to-carat conversion.
Should I include labour cost in cost per carat?
Yes, if you are pricing your work professionally. Many hobby faceters omit labour initially, which can lead to underpricing. The calculator includes an optional labour field. Even a rough figure — estimated hours × your hourly rate — gives you a more accurate break-even picture. Professional faceters often find that labour is the largest component of cost per finished carat on low-value rough.