Carat Weight on a Report, Expressed in Grams
Every figure that matters in a stone deal is a carat figure. The lab report states it, the parcel invoice totals it, the price is quoted per carat — and yet the moment a stone has to be insured, shipped, declared or checked against a general balance, somebody needs the same weight in grams. The relationship is fixed and simple, which is exactly why nobody in the trade bothers to memorise it.
What Sits Behind the Number
Weighed loose, to the third decimal
Weight is not the same as spread
Reports round the figure
Mounted stones are estimated
From a Parcel Figure to Grams and Back
The same three or four keystrokes cover a single certified stone and a bag of melee.
Enter the carat weight as written
Type 0.98, 1.27 or a 14.55 ct parcel total into the left field; grams appear as you type. A comma works instead of a dot, and spaces inside the number are ignored.
Switch the right side to milligrams for melee
Small goods read badly in grams. Search the right-hand dropdown for milligram and a 0.03 ct accent stone shows as 6 mg instead of 0.006 g — a figure you can actually compare.
Copy the plain number for a stock line
The copy button places the bare figure on the clipboard — no unit, no thousands spacing — which is what a stock sheet, an insurance schedule or a shipping declaration field expects. Ctrl + C inside a field does the same.
Reverse it when the scale reads grams
A general balance gives grams, not carats. Press the swap button (↔) to run g → ct: 0.85 g on the pan is 4.25 ct.
Stone Weights, Grams and the Size They Look
The weights that come up daily at the counter, with the diameter a well-proportioned round brilliant of that weight typically measures.
| Carat weight | Grams | Milligrams | Round brilliant ≈ diameter | Where it turns up |
|---|---|---|---|---|
| 0.01 ct (1 point) | 0.002 g | 2 mg | 1.3 mm | Pavé and melee parcels |
| 0.10 ct (10 points) | 0.02 g | 20 mg | 3.0 mm | Halo and accent stones |
| 0.25 ct | 0.05 g | 50 mg | 4.1 mm | Side stones, small solitaires |
| 0.50 ct | 0.1 g | 100 mg | 5.2 mm | The half-carat bracket |
| 1.00 ct | 0.2 g | 200 mg | 6.5 mm | The benchmark centre stone |
| 2.00 ct | 0.4 g | 400 mg | 8.2 mm | Larger centre stone |
| 5.00 ct | 1 g | 1000 mg | 11.0 mm | Statement stone — five carats to the gram |
Notice how little mass is involved. A one-carat diamond, the stone an entire retail category is built around, weighs two tenths of a gram; a hundred pieces of one-point melee together come to a fifth of a gram. Diameter, meanwhile, barely doubles across the whole table — weight climbs with the cube of the size, which is why price does not rise in a straight line either.
What Helps When You Are Handling Goods
Small weights stay legible
Results carry up to eight decimals, so a one-point stone reads 0.002 g rather than collapsing to zero, and a parcel total keeps its thousandths.
Milligrams and grains within reach
Both dropdowns are searchable and list every weight unit, so the same page handles a milligram figure for melee or a grain figure on an old pearl invoice.
Two-way against the pan
The swap button turns the page into a g → ct check, the direction you need when someone hands you a gram reading and quotes a per-carat price.
Figures a document will accept
Copy hands over the clean number, ready for a memo, a customs line or a valuation, with nothing to strip out afterwards.
Carat Weight Questions From the Counter
A dealer says a stone is "fifteen points" — how much is that?
A point is one hundredth of a carat, so a carat is 100 points and fifteen points is 0.15 ct — 0.03 g, or 30 mg. The habit exists because "fifteen points" is faster and less ambiguous across a counter than "nought point one five carats", and because small goods live almost entirely in the first two decimals.
Is the carat of a diamond the same thing as the karat of a gold ring?
No — they are unrelated measures that unfortunately sound identical. Carat (ct) is a mass: 0.2 g, applied to the stone. Karat (K or kt) is a purity fraction in twenty-fourths applied to the metal, so 18K is 18 parts gold in 24, or 75% fine. A one-carat stone in an 18K mount involves both, describing two different objects. British usage spells the purity measure "carat" as well, which is why fineness numbers such as 750 or 999 are safer in writing.
Why is the carat exactly 0.2 g and not some awkward number?
Because it was deliberately redefined to be tidy. The old carat descended from carob-seed weights and drifted from market to market — London, Amsterdam, Florence and Paris all worked to slightly different values, which made cross-border parcels a running argument. The metric carat of 200 mg was agreed internationally from 1907 and written into national law over the following years, the United States adopting it in 1913. Everything since has been one unit worldwide, and the round 0.2 g is the whole point of it.
Why does a 0.98 ct stone sell for so much less than a 1.00 ct?
The trade prices in brackets, and the boundaries sit at round weights — 0.30, 0.50, 0.70, 0.90, 1.00, 1.50 and 2.00 ct. Crossing one lifts the rate per carat, and the total is weight multiplied by that rate, so a stone just under a boundary loses on both factors at once. The physical gap is 0.196 g against 0.200 g: four milligrams, and roughly a tenth of a millimetre on the diameter. Buyers who want the number pay for it; buyers who want the look often shop deliberately just below it.
How is a melee parcel sold if the stones are not weighed individually?
By total carat weight. The parcel goes on the balance as a whole and the price is a per-carat rate for that size range, quality and cut, so the invoice reads something like "14.55 ct" with a stones count beside it. A 5.00 ct parcel of one-point goods is 500 stones and exactly 1 g of diamond; the same 5.00 ct in 0.10 ct sizes is 50 stones and still 1 g. Sizes are described by a millimetre range or by stones-per-carat, and the count matters because setting labour is charged per stone, never per gram.
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