Troy Ounce vs Gram: Gold Weight Conversion
Exact conversion factors for every unit gold is traded in, and the ounce mix-up that inflates estimates by nearly 10%.
Updated June 20, 2026
The two ounces
Precious metals are weighed in troy ounces. Almost everything else sold by weight uses the avoirdupois ounce. A troy ounce is 31.1034768 grams. An avoirdupois ounce is 28.349523 grams. The troy ounce is 9.71% heavier. The naming collision is a historical accident, and it is expensive. If you weigh gold on a postal or kitchen scale set to ounces and multiply by the spot price, your answer is 9.71% too high, every time. On a 10-ounce holding at $4,060 that is roughly $3,900 of imaginary gold. The system has other traps. A troy pound is 12 troy ounces, not 16, so a troy pound is actually lighter than a regular pound. Nobody prices gold in pounds, but the fact tells you the two systems share nothing but the word "ounce".
Exact conversion factors
These are the numbers used across the trade. Troy ounce to grams: multiply by 31.1035. Grams to troy ounces: divide by 31.1035, or multiply by 0.0321507. Pennyweight (dwt): 1 dwt = 1.55517 grams, and 20 dwt = 1 troy ounce. Grain: 1 grain = 0.0647989 grams, and 480 grains = 1 troy ounce. Tola: 1 tola = 11.6638 grams, so a troy ounce is 2.6667 tolas. Thai baht (jewelry): 1 baht = 15.244 grams. Chinese mace: 1 mace = 3.77994 grams. Kilogram: 1 kg = 32.1507 troy ounces. Avoirdupois ounce, for the sake of catching the error: 1 oz avdp = 28.349523 grams = 0.911458 troy ounces. If a scale is reading "oz" and you did not deliberately set it to troy, assume it is avoirdupois.
Conversion table for common weights
Reading across: grams, troy ounces, pennyweights. 1 g = 0.0322 ozt = 0.643 dwt. 5 g = 0.1608 ozt = 3.215 dwt. 10 g = 0.3215 ozt = 6.430 dwt. 20 g = 0.6430 ozt = 12.86 dwt. 31.1035 g = 1 ozt = 20 dwt. 50 g = 1.6075 ozt = 32.15 dwt. 100 g = 3.2151 ozt = 64.30 dwt. 1,000 g = 32.1507 ozt = 643.01 dwt. And in the other direction for the units that show up on jewelry counters: 1 dwt = 1.5552 g. 1 tola = 11.6638 g = 0.375 ozt. 1 baht = 15.244 g = 0.4900 ozt. 1 grain = 0.0648 g.
Why pennyweight persists in the US
Pennyweight is the unit many US jewelers, pawn shops and dental buyers still quote in. It survives partly through inertia and partly because 20 dwt to the troy ounce is easier to do in your head than 31.1 grams. The problem is that it makes offers hard to compare. A dwt is 1.5552 grams, so a per-dwt price is 55.5% larger than the equivalent per-gram price. Set a $76 per gram 14K offer next to a $118 per dwt 14K offer and the second looks dramatically better - they are in fact the same offer. If one buyer quotes dwt and another quotes grams, convert both to grams before comparing. Divide any dwt price by 1.5552 to get the per-gram equivalent.
Tola, baht and regional units
The tola is the standard retail unit across India, Pakistan, Nepal and Bangladesh at 11.6638 grams - historically the weight of a British India silver rupee. Indian gold jewelry is usually 22K, so a tola of jewelry gold contains 11.6638 × 0.9167 = 10.69 grams of fine gold. The Thai baht as a gold weight is 15.244 grams for jewelry and 15.16 grams for bullion bars, and Thai jewelry is conventionally 96.5% gold rather than a karat figure. The Chinese tael and mace, the Japanese momme, and the Middle Eastern dirham as a weight all still appear in local pricing. When you are buying or selling across borders, the unit is as important as the karat. A price quoted per tola for 22K and a price quoted per gram for 18K describe completely different things, and only converting both to fine grams makes them comparable.
Practical rules
Weigh in grams. Grams are unambiguous, convert cleanly to every other unit, and are what almost every jewelry scale defaults to. If your scale has a troy ounce mode, use grams anyway and convert - it removes a whole class of error. Confirm the unit on every quote in writing before you compare. Ask specifically: per gram or per pennyweight, and at what karat. Sanity-check the magnitude. At a $4,060 spot price, pure gold is about $130 per gram, $203 per dwt, and $1,522 per tola. If a quoted number is not in the right neighbourhood for the unit it claims, someone has the conversion wrong.
Key points
1 troy ounce = 31.1035 grams; 1 avoirdupois ounce = 28.3495 grams. Confusing the two overstates gold value by 9.71%. 20 pennyweight = 1 troy ounce; 1 dwt = 1.5552 g. Convert everything to grams before comparing quotes from different buyers.