If you’ve ever wondered why an ounce of gold doesn’t match an ounce of flour, the answer lies in two distinct measurement systems: the everyday avoirdupois ounce and the troy ounce used for precious metals. This guide gives the exact numbers, shows how to convert 1 oz to grams in both systems, and explains why the difference matters for anyone buying or selling gold.

4 related posts

1 standard ounce (oz): 28.3495 grams ·
1 troy ounce (ozt): 31.1035 grams ·
Gold is typically measured in: troy ounces ·
Conversion formula: multiply by 28.3495 (standard) or 31.1035 (troy)

Quick snapshot

1Standard Ounce
2Troy Ounce
  • Used for precious metals (BullionVault (precious metals exchange))
  • 1 troy oz = 31.1035 grams (Wikipedia (open encyclopedia))
  • Originates from medieval French trade (Wikipedia (open encyclopedia))
3Gold Ounce
4Conversion Tips

Two systems, one confusing world. Here are the key numbers you need to remember.

Measurement Value in grams Used for
1 standard ounce (avoirdupois) 28.3495 grams (Wikipedia (open encyclopedia)) Food, household, body weight
1 troy ounce 31.1035 grams (Wikipedia (open encyclopedia)) Gold, silver, platinum, palladium
1 ounce of 24K gold (troy) 31.1035 grams Gold bullion and coins
30 grams in ounces 1.0582 standard oz (approx) General conversion
Gold purity conversion 24K = 99.9% gold, 22K = 91.7% (JM Bullion (precious metals dealer)) Purity impact on price per gram

How many grams are in 1 oz?

For the standard ounce — the one you see on food labels and bathroom scales — the answer is 28.3495 grams. The international avoirdupois ounce is defined as exactly 28.349523125 grams (Wikipedia (open encyclopedia)). For practical purposes, 28.35 is close enough for most kitchen scales, but scientific and trading applications demand more precision.

Standard ounce to gram formula

Bottom line: For anyone weighing everyday items, the standard ounce is the unit to use. Multiply ounces by 28.35 to get grams; using the wrong conversion would undercount or overcount your measurements. It is defined as exactly 28.349523125 grams.
  • Formula: grams = ounces × 28.349523125
  • Rounded shorthand: grams = ounces × 28.35
  • Reverse: ounces = grams ÷ 28.349523125
  1. Identify which ounce system: standard or troy.
  2. Multiply the number of ounces by the conversion factor (28.3495 for standard, 31.1035 for troy).
  3. Round to desired precision.

To convert 1 oz to grams manually, simply multiply 1 × 28.349523125 = 28.3495 g. Online converters like Metric Conversions do the work instantly, but knowing the factor helps you verify results.

Quick conversion table for common ounce values

Six common weights, one pattern: the difference grows as the weight increases.

Ounces (standard) Grams (exact) Grams (rounded)
0.5 oz 14.1748 g 14.17 g
1 oz 28.3495 g 28.35 g
2 oz 56.6990 g 56.70 g
5 oz 141.7476 g 141.75 g
10 oz 283.4952 g 283.50 g
16 oz (1 lb) 453.5924 g 453.59 g

The implication: When a recipe or product label says “1 oz”, assume the standard ounce unless you’re dealing with metals. That 28.35 g baseline is reliable for nearly all consumer goods.

The catch

Many kitchen scales default to a conversion factor of 28.35 g/oz, which works fine for cooking but not for gold. If you weigh a gold coin on a kitchen scale, you’ll get 28.35 g, but a dealer’s troy scale will read 31.10 g — a 9.7% discrepancy that can cost you real money.

The bottom line: accurate measurement depends on knowing which ounce is in play.

Is 1 ounce 31.1 grams?

Only if you’re talking about a troy ounce. The standard ounce is 28.3495 g, but a troy ounce — the unit used for gold, silver, platinum, and palladium — equals 31.1035 grams (Wikipedia (open encyclopedia)). That’s about 9.7% heavier (BullionVault (precious metals exchange)).

Difference between standard ounce and troy ounce

Three key contrasts, one takeaway: never assume which ounce is being used.

Feature Standard (avoirdupois) ounce Troy ounce
Grams per ounce 28.349523125 (Wikipedia (open encyclopedia)) 31.1034768 (Wikipedia (open encyclopedia))
Grains per ounce 437.5 (Wikipedia (open encyclopedia)) 480 (Wikipedia (open encyclopedia))
Pounds per system 16 oz per lb (Wikipedia (open encyclopedia)) 12 oz per troy lb (Wikipedia (open encyclopedia))
Primary use Food, household, body weight Precious metals (BullionVault (precious metals exchange))

Why gold uses troy ounces

The precious-metals industry adopted the troy ounce centuries ago, and it remains the global standard for pricing and trading gold, silver, platinum, and palladium (BullionVault (precious metals exchange)). The London Bullion Market Association (LBMA) and all major exchanges quote gold in troy ounces. When you see “gold price per ounce” on financial news, it’s always a troy ounce.

“The precious-metals industry commonly uses troy ounces for gold, silver, platinum, and palladium.”

BullionVault (precious metals exchange)

What this means: If you buy a “1 oz” gold coin, you’re getting 31.1 g of gold, not 28.3 g. Confusing the two could lead to overpaying or undervaluing your metal by nearly 10%.

Why this matters

A gold investor who mistakenly uses standard ounces to calculate grams will underestimate their gold weight by 9.7%. On a $2,000/oz gold purchase, that’s a $194 miscalculation — enough to turn a profitable trade into a loss.

Bottom line: The pattern: always verify which ounce is being referenced before making any trade or purchase.

Why is 1 oz gold 31 grams?

Because gold is measured in troy ounces, not standard ounces. The troy ounce has roots in the Roman monetary system and was standardized in medieval France (Wikipedia (open encyclopedia)). Its exact conversion is 31.1034768 grams — often rounded to 31.1035 or simply 31.1 g.

History of the troy ounce

  • The troy system derives from the Roman uncia and was later adopted at the fair of Troyes, France (Wikipedia (open encyclopedia)).
  • One troy ounce equals 480 grains, and since the 1959 international yard and pound agreement, one grain is defined as exactly 64.79891 milligrams (Wikipedia (open encyclopedia)).
  • The troy pound contains 12 troy ounces, unlike the avoirdupois pound of 16 ounces (Wikipedia (open encyclopedia)).

How the troy ounce became standard for gold

By the 19th century, London had become the world’s gold trading hub, and the troy ounce was already entrenched in British coinage. The LPPM (London Platinum and Palladium Market authority) continues to use the troy system today, cementing it as the global benchmark.

“1 Troy Ounce = 31.1035 Grams”

Bullion Standard (precious metals guide)

The pattern: Tradition, not logic, keeps the troy ounce alive. But in an industry where contracts and prices depend on precise weight, that tradition is non-negotiable.

The trade-off

Newer digital scales can switch between units, but the market itself is locked into troy ounces. Any move to metricate gold trading would require rewriting centuries of contracts, pricing formulas, and refiner specifications — a change that benefits no one except converters.

The implication: investors and traders must adhere to the troy standard or risk miscalculation.

How many grams are in an ounce of gold?

A single troy ounce of gold — no matter the purity — weighs 31.1035 grams (Wikipedia (open encyclopedia)). Purity affects value, not weight: 24K gold (99.9% pure) weighs the same as 22K gold (91.7% pure) for the same troy ounce.

Confirmed facts

  • 1 standard oz = 28.349523125 grams (Wikipedia (open encyclopedia))
  • 1 troy oz = 31.1034768 grams (Wikipedia (open encyclopedia))

What’s unclear

  • A troy ounce is about 9.7% heavier than a standard ounce (JM Bullion (precious metals dealer))
  • Gold is traded in troy ounces globally (BullionVault (precious metals exchange))
  • The exact historical origin of the troy ounce is not fully documented (Wikipedia (open encyclopedia))
  • Long-term gold price predictions involve uncertainty (BullionVault (precious metals exchange))

24K gold weight

Pure gold — 24 karat or 99.9% — contains no alloyed metals. A one-troy-ounce 24K gold bar weighs exactly 31.1035 grams. The same weight applies to 22K, 18K, or any other karat; purity only changes the gold content, not the total mass (JM Bullion (precious metals dealer)).

Gold purity and weight implications

  • Price per gram vs per ounce: Gold is often quoted per troy ounce, but small buyers may see per-gram prices. To convert, divide the per-ounce price by 31.1035.
  • Weight consistency: A 1 oz gold coin from any mint weighs the same — 31.1035 g — because the industry enforces the troy standard.
  • Kitchen scale warning: Using a standard-ounce scale will under-read your gold by 9.7%. Always use a troy scale or convert the reading.

The pattern: purity changes value, not weight; the troy ounce is the constant.

What if I invested $1000 in gold 10 years ago?

Gold prices are notoriously volatile, but long-term trends have rewarded patient investors. According to BullionVault (precious metals exchange), gold is traded in troy ounces and its price has risen significantly over the past decade. However, the exact return depends on the purchase and sale dates — timing matters as much as the weight conversion.

Gold price performance over the past decade

Rather than cite a specific number (which may not reflect your buy/sell window), focus on the key factors that drive gold’s value: inflation, interest rates, geopolitical instability, and industrial demand. The LPPM (London Platinum and Palladium Market authority) provides daily fixings for gold in troy ounces. A $1,000 investment in 2015, when gold was around $1,060 per troy ounce, would have bought roughly 0.94 troy ounces. At today’s prices near $2,400 per troy ounce, those ounces would be worth about $2,256 — a gain of over 125%. But past performance is no guarantee of future returns.

Return on investment for gold

The trade-off: Gold is a hedge, not a dividend payer. Its value lies in preservation, not income. For investors who bought at the 2015 trough and sold at the 2024 peak, the ROI has been substantial. But those who bought at the 2011 peak ($1,900/oz) took years to break even.

Additional sources

en.wikipedia.org, bullion.com

För den som vill fördjupa sig i skillnaden mellan standard och troy ounce finns det en utförlig guide som går igenom båda måttenheterna.

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Frequently asked questions

Do gold dealers use standard or troy ounces?

Gold dealers exclusively use troy ounces. When you see a gold bar labeled “1 oz”, it means 1 troy ounce (31.1035 g). Always confirm the unit with your dealer.

How do I convert grams to ounces?

Divide the number of grams by 28.3495 to get standard ounces, or divide by 31.1035 to get troy ounces. Use an online converter for speed.

What is the weight of a gold bar in grams?

A standard 1-troy-ounce gold bar weighs 31.1035 grams. Larger bars, like the 400 oz “good delivery” bar, weigh about 12.44 kg (12,441.4 g).

Can I use a kitchen scale to weigh gold?

You can, but only if you set it to grams and then divide by 31.1035 to get troy ounces. Most kitchen scales default to standard ounces, which will give you a 9.7% undercount.

Why are there two different ounce measurements?

Historical accident. The avoirdupois system evolved for general trade, while the troy system was specialized for precious metals, gems, and apothecary weights. They remain separate because switching would disrupt centuries of established practice.

Related reading

For anyone buying or selling gold, the rule is simple: always ask which ounce your dealer is using. A troy ounce gives you 31.1035 grams; a standard ounce gives you only 28.3495 grams. Mistaking one for the other means losing 9.7% of your gold weight — or overpaying the same amount. For gold buyers, the choice is clear: insist on troy ounces, or use grams as the universal reference to avoid confusion.