Two units share a name and differ by nearly a tenth. Mixing them up is the most expensive arithmetic error in this whole subject.
The numbers
Every weight unit used in the precious metals trade, in grams.
Unit
Grams
Gold at this weight
1 grams
1
$132.89
1 pennyweight
1.55517384
$206.66
1 troy ounces
31.1034768
$4,133
1 ounces
28.349523125
$3,767
1 kilograms
1000
$132,888
1 grains
0.06479891
$8.61
A troy ounce is 31.1034768 grams. The ounce on a kitchen scale, the avoirdupois ounce, is
28.349523125 grams. The troy ounce is 9.714% heavier, and that percentage is the whole of the
problem.
Why the mistake costs money
Suppose you weigh a bar on a kitchen scale, read 10 ounces, and price it at the gold quote of
$4,133.30 an ounce. You have just valued
283.5 grams of gold at the price of 311 grams. The overstatement is
$3,659 on that one calculation, and you walk into the shop expecting a number nobody is going to
say.
The error runs the other way just as easily. A seller who converts a troy ounce price into a
kitchen ounce weight underprices their own metal by the same 9.7%. The calculator on this site
carries both units for exactly this reason: set the unit to match the scale you actually used,
not to the word you heard quoted.
The pennyweight
A pennyweight, written dwt, is one twentieth of a troy ounce: 1.55517384 grams. It comes from
the weight of a medieval English silver penny, and it survives because the American jewellery
trade has always used it. Twenty pennyweights make a troy ounce, and 240 made a troy pound,
which is where 240 pence to the pound sterling came from.
It matters today for one reason: a price quoted per pennyweight is 1.555 times the equivalent
price per gram, so it sounds better than it is. A buyer offering a per pennyweight figure is
not necessarily being deceptive, since that is genuinely how their trade quotes, but you cannot
compare it to a gram quote without dividing. Do the division before you decide anything.
Troy pounds, grains and the rest
A troy pound is 12 troy ounces, 373.24 grams, and is lighter than the 453.59 gram avoirdupois
pound despite the troy ounce being heavier. It is effectively obsolete. A grain, 0.06479891
grams, survives in the bullet and gemstone trades and occasionally on old scales. A carat, for
stones, is 0.2 grams and has nothing to do with the karat of gold beyond an ancestral link to
carob seeds.
The one rule
Weigh in grams, price in grams, and convert only at the end. Grams are unambiguous, every
digital scale reads them, and the conversion to any other unit is a single multiplication that
you can do once at the finish rather than repeatedly in the middle. Every figure on this site is
computed in grams underneath, whatever unit you asked it to display.
Unit questions
What is a troy ounce?+
A unit of 31.1034768 grams, used for precious metals and for essentially nothing else. Every gold, silver, platinum and palladium price you will see quoted is per troy ounce.
How many grams are in a troy ounce?+
31.1034768 grams exactly. The ordinary avoirdupois ounce is 28.349523125 grams. The troy ounce is about 9.7% heavier.
Is a troy ounce heavier than a regular ounce?+
Yes, by roughly a tenth. Confusingly, a troy pound is lighter than a regular pound, because a troy pound is 12 troy ounces rather than 16 ounces. That is why nobody in the metals trade uses pounds.
What is a pennyweight?+
One twentieth of a troy ounce, 1.55517384 grams, abbreviated dwt. It is the traditional unit of the American jewellery trade and many buyers still quote in it.
How do I convert a price per pennyweight to a price per gram?+
Divide by 1.55517384. A quote of $45 per pennyweight is $28.94 per gram. Always convert before comparing two offers, because a pennyweight price looks more than half as large again as the equivalent gram price.
Which unit should I weigh my gold in?+
Grams, on a scale reading to 0.1 g. It is the finest common unit, most scales default to it, and every conversion is easy from there. Just make sure the calculator is set to grams as well.
Do jewellers use troy ounces?+
They buy and sell metal in troy ounces and pennyweights and often weigh customer items in grams. Expect to hear all three in one conversation, and ask which unit any quoted price refers to.
Recommended Gold Testing & Smelting Equipment
Laboratory-grade scales, non-destructive electronic testers, and digital melting furnaces for accurate scrap valuation and refining.
Digital Electric Gold & Silver Melting Furnace (1kg to 3kg, 1150°C / 2100°F)
Commercial digital smelting furnace with high-density graphite crucible, insulated heating chamber, and heavy-duty crucible tongs. Heats up to 2100°F (1150°C) with precise digital PID temperature control to cleanly melt scrap gold jewelry, sterling silver, and brass into tradeable bullion bars in under 45 minutes.
Laboratory-grade electronic gold analyzer that instantly determines karat purity from 10K to 24K and verifies platinum without messy acid drops or destructive scratching. Rapid self-calibration ensures quick, reliable scrap valuation without damaging collectible jewelry.
0.001g High-Precision Analytical Milligram Jewelry Scale (50g x 0.001g)
Laboratory-grade analytical milligram balance measuring down to 0.001 grams, 0.005 carats, and 0.0001 troy ounces (ozt). Features a clear protective draft shield, tare function, and stainless steel calibration weights to catch fine weight fractions before smelting.
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Machined high-purity fine-grain graphite mold designed for pouring clean 1 oz, 2 oz, 5 oz, and 10 oz gold and silver bars. Delivers high thermal stability, rapid heat dissipation, and a smooth cavity finish for effortless ingot release.
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Compare essential equipment specifications for establishing an efficient scrap gold testing and melting workstation:
Equipment Type
Primary Purpose
Capacity / Accuracy
Key Advantage
Electric Smelting Furnace
Melting scrap jewelry, dental gold, and coins into bullion
1 kg to 3 kg crucible capacity
Clean flameless PID temperature control up to 2100°F
Electronic Karat Tester
Instant purity check on intact jewelry and high-end watches
10K to 24K gold and platinum ranges
Non-destructive testing with no acid stains or scratches
Analytical Milligram Scale
Precise scrap weight measurement before refining
50g capacity at 0.001g (0.0001 ozt)
Catches fine weight margins standard kitchen scales miss
Multi-Cavity Ingot Mold
Casting molten scrap metal into tradeable bullion bars
1 oz, 2 oz, 5 oz, 10 oz bar cavities
High-density graphite prevents sticking and oxidation
Acid Touchstone Assay Kit
Distinguishing solid karat alloy from heavy vermeil or plate
10K, 14K, 18K, 22K acid standards
Time-tested chemical confirmation for scrap buyers
Scrap Valuation Pro Tip: Melt Loss & Non-Destructive Testing
When melting scrap jewelry lots, expect an average 1% to 3% melt loss due to burn-off of non-precious solder joints, skin oils, and enamel. Before melting high-value items, verify karat content using a non-destructive electronic tester. Acid scratch testing can leave noticeable etch marks and may read false positive on heavy gold-filled or rolled gold plate items (such as 1/10 10K RGP or vermeil).
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