Troy Ounces, Gold Pricing, and Why Precious Metals Use a Different Weight System
A troy ounce (31.1g) is 9.7% heavier than an everyday ounce (28.35g) — and all precious metal pricing uses the troy system. Here's how gold prices work per gram and per tola, the three weight systems compared, and why karat means two completely different things.
By sadiqbd · June 9, 2026
Gold is priced in troy ounces — a measurement system most people have never used for anything else
A troy ounce of gold is not the same as the ounce in your kitchen. It's heavier — 31.1 grams versus the 28.35 grams of an avoirdupois ounce. This difference of 2.75 grams doesn't sound significant until you're tracking the price of gold, silver, or platinum, at which point using the wrong ounce creates an error of about 10% in every calculation.
The troy system is a historical survival — maintained specifically because precious metals and gemstones require a consistent standard across centuries of trading, and the troy system was already embedded in centuries of market convention.
The three weight systems
Most of the world uses two overlapping systems for mass and weight:
Metric (SI): grams, kilograms, metric tonnes. The global scientific and commercial standard.
Avoirdupois: the everyday US/UK imperial system for general goods. 16 ounces = 1 pound; 14 pounds = 1 stone; 2,240 pounds = 1 long ton. Used for body weight, food, and most commercial goods.
Troy: specifically for precious metals and gemstones. 12 troy ounces = 1 troy pound (unusual — 16 ounces = 1 pound in avoirdupois). The troy pound is lighter than the avoirdupois pound, but the troy ounce is heavier than the avoirdupois ounce.
Key comparison:
| Unit | Grams |
|---|---|
| 1 troy ounce (ozt) | 31.103 g |
| 1 avoirdupois ounce (oz) | 28.350 g |
| 1 troy pound (12 troy oz) | 373.24 g |
| 1 avoirdupois pound (16 oz) | 453.59 g |
The troy ounce is about 9.7% heavier than the avoirdupois ounce. A "1 pound" weight in troy system is lighter than a "1 pound" in everyday use.
How gold prices work
Spot price: the current market price for immediate delivery of physical gold. Quoted globally in USD per troy ounce. Updated continuously during market hours.
Common reference: the London Bullion Market Association (LBMA) publishes a benchmark price twice daily (AM and PM gold fixes) used as a global reference point.
Gold price in other units (illustrative at $2,000/troy oz):
- Per gram: $2,000 ÷ 31.103 = $64.30/g
- Per kilogram: $64.30 × 1,000 = $64,300/kg
- Per avoirdupois ounce (28.35g): $64.30 × 28.35 = $1,822/oz (avoid this confusion — always use troy oz for gold pricing)
- Per tola (11.664g, South Asian measurement): $64.30 × 11.664 = $749.9/tola
The tola: a traditional South Asian weight unit equal to 3/8 troy ounce (11.664g). Still used for gold trading in India, Pakistan, Bangladesh, and the Gulf. Gold jewellery and investment products in South Asia are frequently quoted in tolas.
Silver, platinum, and other precious metals
The same troy weight system applies to all precious metals:
Silver: quoted in USD per troy ounce. Much lower price than gold (silver-to-gold ratio has historically varied from 15:1 to over 90:1). Silver is more industrial (electronics, solar panels, medical applications) than gold, making its price more responsive to industrial demand.
Platinum: also quoted in troy ounces. Platinum is rarer than gold but has historically traded at both higher and lower prices depending on automotive demand (catalytic converters) and mine supply. South Africa produces about 70% of global platinum.
Palladium: priced per troy ounce. Primarily used in catalytic converters for petrol engines. Briefly more expensive than gold in 2020–2021 due to supply constraints and automotive demand.
Rhodium: extremely rare and expensive. Priced per troy ounce. Industrial use in catalytic converters. Prices have reached $20,000–$30,000 per troy ounce in periods of supply constraint.
Gold bars and coins: standard denominations
Gold is traded and stored in standardised forms:
Good Delivery Bar (London standard):
- Weight: 350–430 troy ounces (approximately 12–13 kg)
- Purity: minimum 99.5% (995 fineness)
- Used for central bank reserves and institutional settlement
Kilo bar: 1 kg = 32.15 troy ounces. Common for retail and mid-size investors.
Sovereign coin: British gold sovereign contains exactly 0.2354 troy ounces of gold (7.322g of gold in 22-carat alloy). Legal tender face value of £1, actual gold value many times higher.
American Gold Eagle: 1 troy ounce in the 1 oz coin; also available in ½, ¼, and 1/10 oz. US legal tender.
Canadian Gold Maple Leaf: 99.99% pure gold. Available in 1 oz and smaller denominations.
Carats in gold and gemstones
Gold purity (karats, US spelling; carats elsewhere): 24-karat gold = pure gold (99.9%+) 18-karat gold = 18/24 = 75% gold 14-karat gold = 14/24 = 58.3% gold 9-karat gold (UK minimum for hallmarking) = 37.5% gold
Gemstone weight (carats, different unit): 1 carat (ct) = 200 milligrams = 0.2 grams. Used for diamonds and other gemstones. Origin: historically the seed of the carob tree, which has remarkably consistent weight.
These two uses of "carat" are completely different measurements — gold purity and gemstone weight — using the same word.
How to use the Weight Converter on sadiqbd.com
- Enter the weight and source unit — grams, kilograms, troy ounces, avoirdupois ounces, pounds, stone, tolas, metric tonnes
- Convert — see equivalents across all weight units
- Apply to precious metals — convert gold prices between troy ounces and grams for comparison
Frequently Asked Questions
Why is gold still quoted in troy ounces instead of kilograms? Historical convention embedded in centuries of market infrastructure. Contracts, futures markets, exchange standards, and most gold-related pricing systems globally use troy ounces. Changing would require coordinated change across all markets simultaneously — the switching cost is high with limited benefit.
How is stone weight used and where? Stone (14 pounds avoirdupois = 6.35 kg) is used almost exclusively in the UK and Ireland for body weight. "I weigh 12 stone 4" (12 × 14 + 4 = 172 pounds = 78 kg). No other country uses stone; even the UK uses kg for most official purposes.
Is the Weight Converter free? Yes — completely free, no sign-up required.
Troy weight is a medieval trading standard that survived because precious metal markets have no reason to change a system that works. Understanding it — and how it differs from everyday ounces — prevents 10% errors in every gold calculation.
Try the Weight Converter free at sadiqbd.com — convert between grams, kilograms, troy ounces, pounds, stone, and tolas instantly.
