Price per Carat Calculator
Quick answer
Total price = price per carat x carat weight, then minus any discount and plus tax. A 2.40 ct stone at 450 per carat costs 1,080.00. With 15% off and 8% tax it is 991.44. Price per gram is five times the price per carat.
Arithmetic only, not a valuation or price guide. Data verified .
Price per carat to total price
How per-carat pricing works
Loose gems are usually quoted as a rate per carat. The seller multiplies that rate by the stone's weight to get the price. A 0.85 ct stone at 1,200 per carat costs 1,020.00. The rate already reflects everything about the stone: its color, clarity, cut, origin, any treatment, and the market for that size.
This calculator does the arithmetic so you can compare offers quickly and check an invoice. It does not know anything about value, and it never will. That is a job for a qualified appraiser or the market.
Worked example
A dealer quotes 450 per carat for a 2.40 ct stone. The subtotal is 450 x 2.40 = 1,080.00. A 15% discount takes off 162.00, leaving 918.00. Tax of 8% adds 73.44, for a total of 991.44. The effective price per carat after all of that is 413.10.
Price per gram
Rough, beads and cabochon lots are often sold by the gram. Since 1 g = 5 ct, divide a per-gram price by 5 to compare it with a per-carat price, or multiply a per-carat price by 5 to get the per-gram figure. The calculator shows the per-gram rate for you. Read the carat to gram converter page for the other units.
Things that change the rate per carat
- Size jumps. Rates often step up at round numbers, so a stone just under 1 ct can be noticeably cheaper per carat than one just over.
- Lots versus single stones. Parcels of small stones are priced per carat for the whole lot, usually lower than single matched stones.
- Real weight versus DEW. Moissanite prices are often per DEW carat. Ask which weight the rate uses.
- Treatments and origin. These change rates a lot and are best confirmed with a lab report.
Using it as a seller
If you sell stones or jewellery online, write the price per carat and the weight in your listing notes, and make sure the weight is the real weighed weight, not an estimate. If you only have measurements, say so plainly and give the estimate as approximate. The mm to carat calculator gives you a range you can quote honestly.
Important limits
Currency symbols are cosmetic. The calculator does not convert currencies, apply exchange rates or know any local tax rules. Prices in this page's examples are made-up round numbers chosen to show the arithmetic, not real market prices. For anything involving value, insurance or resale, get an independent appraisal.
Related questions
How do you calculate price per carat?
Divide the total price by the carat weight. A 2.40 ct stone priced at 1,080 is 450 per carat. To go the other way, multiply price per carat by weight.
Why are gems priced per carat?
Weight is the one property every stone has in common, so dealers quote a rate per carat and multiply. The rate itself depends on quality, size, origin, treatment and the market.
Does price per carat stay the same for bigger stones?
Usually not. Larger stones are rarer, so the rate per carat often jumps at popular weights such as 0.50, 1.00 and 2.00 ct. Never assume a 2 ct stone costs twice a 1 ct stone.
Is the discount applied before or after tax?
This calculator applies the discount first, then tax on the discounted amount, which is how most shops work. Check your own local rules.
How do I convert price per gram to price per carat?
Divide the price per gram by 5, because 1 gram is 5 carats. The calculator shows price per gram for you.
Can this tell me what my stone is worth?
No. It only multiplies numbers you enter. Value depends on quality factors that a calculator cannot see. For value, consult a qualified, independent appraiser.
What weight should I use for moissanite sold by DEW?
Use whatever weight the seller priced on, and ask which one it is. A rate per DEW carat and a rate per real carat are not comparable.
Should I compare price per carat across different gems?
Only loosely. A carat of emerald and a carat of sapphire are different sizes, so price per millimetre of face-up size can be a fairer comparison when shopping for a look.
Sources and method
Weight estimates use the colored-stone shape factors published by the International Gem Society and the Dendritics standard formula, and the diamond trade constants and length to width ratio tables published in jewelry trade references (Esslinger, Omni, Octonus). Specific gravity values are cross-checked against the International Gem Society density tables, the USGS Natural Gemstones report and GemSelect.
Every number on this page is generated by the same formula engine as the calculators. Read the full method, constants and limits and the editorial policy. Data last verified 2026-11-04.
Estimates only. This is not an appraisal, grading report or valuation. A calibrated scale or a lab report is the only real weight.