Troy Ounce vs Gram: How Gold Prices Are Calculated

Gold prices are quoted everywhere in dollars per ounce — but that “ounce” isn’t the one on your kitchen scale. If you’ve ever tried to work out what a gold ring, coin or small bar is actually worth, you need to understand troy ounces, grams and karats. Here’s a clear guide.

You can follow live numbers on our gold price page.

What is a troy ounce?

Precious metals are weighed in troy ounces. One troy ounce equals about 31.1035 grams. The ordinary (avoirdupois) ounce used for food and everyday goods is lighter, at about 28.35 grams. So a troy ounce of gold weighs roughly 10% more than a “regular” ounce.

The troy system takes its name from Troyes, a medieval trading town in France, and has been the standard for precious metals for centuries. Twelve troy ounces make a troy pound, though the troy pound is rarely used today.

What sets the spot price of gold?

The spot price is the current market price for gold for immediate delivery, set by trading in major markets such as London, New York and Shanghai. Key drivers include:

• Real interest rates: when inflation-adjusted yields fall, holding non-yielding gold becomes more attractive.
• The US dollar: gold is priced in dollars, so a weaker dollar often lifts the gold price.
• Central bank purchases: reserve diversification by central banks is a major source of demand.
• Uncertainty: financial stress and geopolitical tension tend to push investors toward gold.
• Jewelry and industrial demand.

Converting the price: ounce, gram and kilogram

Price per gram = Spot price per troy ounce ÷ 31.1035 Price per kilogram = Price per gram × 1,000 (≈ 32.15 troy ounces)

Example: with gold at $4,000 per troy ounce (illustrative):

• Per gram: 4,000 ÷ 31.1035 ≈ $128.60
• Per kilogram: ≈ $128,600

To convert into another currency, multiply by the exchange rate — or use our currency converter, which includes gold by the ounce and gram.

Karats and purity

Karat (k) measures how much of an item is pure gold, out of 24 parts:

Melt value of jewelry

To estimate the raw gold value of a piece of jewelry:

Melt value = Weight (g) × Purity × Price per gram

A 10-gram 14k chain at $128.60/g: 10 × 0.585 × 128.60 ≈ $752. Expect a buyer to offer less than melt value, since refiners and dealers need a margin — and jewelry’s retail price includes design and labor you usually won’t recover.

Popular coins and their gold content

Many bullion coins contain exactly one troy ounce of pure gold, even if their total weight is higher because of alloy:

• American Gold Eagle: 1 troy oz of gold in a 22k coin
• Canadian Gold Maple Leaf: 1 troy oz, .9999 fine
• South African Krugerrand: 1 troy oz of gold in a 22k coin
• British Sovereign: about 0.2354 troy oz of gold

Spot price vs what you pay

Dealers sell coins and bars at a premium over spot and buy them back slightly below spot. Smaller sizes usually carry higher premiums per ounce. Gold ETFs track the spot price closely with a small annual expense ratio, which is why many investors use them for price exposure. Compare the options in our gold investing guide.

Silver works the same way

Silver is also priced per troy ounce, so the same formulas apply: divide the spot price by 31.1035 for the price per gram.

Conclusion

Once you know that a troy ounce is about 31.1 grams and that karats measure purity out of 24, converting gold prices becomes simple arithmetic. Use these formulas to sanity-check dealer quotes, estimate the melt value of jewelry and compare coins and bars on a like-for-like basis.