The same word—”ounce”—can mean two completely different weights depending on what you’re buying. If you’re comparing gold to groceries, a single “1 oz” can swing by nearly 2.75 grams. This guide settles the confusion with exact numbers, a quick-reference table, and a step-by-step conversion walkthrough you can use right now.

4 related posts

1 avoirdupois oz: 28.34952g · 1 troy oz (gold): 31.1034768g · Difference: 10% heavier for troy · Common gold oz: 31.1g approx · 4 oz avoirdupois: 113.398g

Quick snapshot

1Confirmed facts
2What’s unclear
  • Exact gold investment returns over specific timeframes require live market data
3Timeline signal
  • Troy system standardized for precious metals by the medieval period
  • Modern value fixed at 31.1034768g in the 19th century
4What’s next
  • Global gold markets continue using troy ounces as the universal pricing standard
Unit Grams Source
Avoirdupois oz to g 28.34952 MGS Refining
Troy oz to g 31.1034768 Conversion.org
Gold bar standard 1 troy oz Provident Metals
1 oz gold approx 31.1g WallStreetMojo

Is 1 oz 28 or 31 grams?

Both — it depends entirely on which ounce system you’re talking about. Three systems matter here, but two dominate everyday life: the avoirdupois ounce (what your kitchen scale uses) and the troy ounce (what gold dealers use). MGS Refining breaks down exactly how they differ.

Avoirdupois ounce (everyday)

  • Standard ounce for cooking, postal packages, and most non-precious items
  • Equals 28.34952312 grams exactly (The Calculator Site)
  • 1 pound avoirdupois = 16 oz avoirdupois = 453.592 grams (Only Gold)

Troy ounce (precious metals)

  • Used for gold, silver, platinum, and other precious metals
  • Equals 31.1034768 grams (Conversion.org)
  • 1 troy pound = 12 troy oz = 373.242 grams (MGS Refining)
The upshot

One troy ounce is roughly 10% heavier than one avoirdupois ounce. A 1-oz gold bar contains about 2.75 grams more gold than you’d get if you measured it on a kitchen scale set to “1 oz.”

What is the Troy Ounce?

The troy ounce is the global standard for weighing precious metals, adopted from the medieval Troyes trade fairs in France. Bold Precious Metals traces the system’s origins back to 12th-century merchant markets where honest weight measurement was critical for trade.

History and definition

  • Troy system originated at medieval Troyes trade fairs, France (Bold Precious Metals)
  • 1 troy ounce = 480 grains (Only Gold)
  • 1 avoirdupois ounce = 437.5 grains (Only Gold)
  • 1 troy ounce = 1.0971 avoirdupois ounces (Only Gold)

Use in gold and silver

  • Gold bullion is priced per troy ounce globally (Free Bullion Guide)
  • Silver, platinum, and palladium follow the same standard
  • Copper and base metals are priced per avoirdupois pound instead (Free Bullion Guide)
  • 20 pennyweights = 1 troy ounce (Maguire Ref)
Why this matters

Jewelers and pawn shops sometimes quote prices in pennyweights (dwt). If you’re selling gold, knowing that 1 dwt = 1.555 grams helps you verify you’re getting fair value.

How many grams is an ounce of 24K gold?

A 24-karat gold bar weighing 1 troy ounce contains exactly 31.1034768 grams of pure gold — purity doesn’t affect the weight, only the composition. WallStreetMojo confirms this figure and notes that the conversion factor has been standardized since the 19th century.

Troy standard for gold

  • All major gold exchanges — COMEX, LBMA, and OTC markets — price gold in troy ounces (Provident Metals)
  • A 1-kilogram gold bar = 32.1507 troy ounces
  • Common retail sizes: 1 oz, 10 oz, 100 g, 1 kg bars all reference the troy ounce

Conversion formula

  • To convert troy ounces to grams: multiply by 31.1035 (WallStreetMojo)
  • Precise formula: Grams = Troy Ounces × 31.10352185 (Metric Conversions)
  • Reverse: 1 gram = 0.032151 troy ounces

Why is an ounce of gold 31 grams?

Gold isn’t measured in “31 grams” by accident — it’s measured in 31.1034768 grams because that’s the definition of a troy ounce. MGS Refining explains that the troy system survived metrication because the global gold market had already standardized around it.

Troy vs avoirdupois explained

  • Troy ounce: 31.1034768g — 480 grains per ounce
  • Avoirdupois ounce: 28.3495g — 437.5 grains per ounce
  • Troy pound (12 oz) is actually lighter than avoirdupois pound (16 oz): 373.242g vs 453.592g (MGS Refining)

Industry standard

  • Switching gold pricing to metric would require global coordination that bullion markets won’t undertake
  • Historical continuity gives troy ounce legitimacy in legal and financial contexts
  • For gold: always use troy ounces to avoid confusion (Free Bullion Guide)
Bottom line: Gold investors pay for 31.1034768g per troy ounce, not the 28.35g kitchen-scale ounce. A buyer who confuses the two is overpaying by roughly 10% on every purchase.

Is 30g equal to 1 oz?

No — and this is one of the most common conversion myths that costs gold buyers money. Neither ounce type rounds to 30 grams, but the troy ounce gets closer. Traditional Oven shows exactly why a simple “30g ≈ 1 oz” shortcut fails in both directions.

Close approximation

  • 30g ÷ 28.3495 = 1.058 avoirdupois oz (kitchen scale says “1 oz” is actually 1.06 oz)
  • 30g ÷ 31.1035 = 0.964 troy oz (gold scale says “1 oz” is actually 0.96 oz)
  • Neither lands on exactly 1 oz — the difference matters for precise weighing

Exact values

  • 1 avoirdupois oz = 28.34952312g — 30g is 1.65g short
  • 1 troy oz = 31.1034768g — 30g is 1.10g short
  • If you measure gold at “30g” on a kitchen scale, you’ve actually weighed less than a troy ounce
The catch

Kitchen scales and postal scales use avoirdupois ounces. Selling gold and quoting its weight in the same units your scale displays will systematically understate the troy ounce value by about 2.75 grams per ounce.

Conversion Table: Avoirdupois vs Troy Ounces to Grams

Six common weights, two systems — here is how the numbers compare side by side so you can see the gap widen as quantities increase.

Quantity Avoirdupois (g) Troy (g) Difference (g)
½ oz 14.17g 15.55g 1.38g
1 oz 28.35g 31.10g 2.75g
2 oz 56.70g 62.21g 5.51g
4 oz 113.40g 124.41g 11.01g
5 oz 141.75g 155.52g 13.77g
10 oz 283.50g 311.03g 27.53g
100 oz 2,835.0g 3,110.3g 275.3g

The pattern here is linear and compounding: at small quantities the 2.75g gap seems minor, but scale it to 100 troy ounces and you’re looking at over 275 grams of unaccounted weight if you used the wrong system.

Step-by-Step: How to Convert Ounces to Grams Manually

You don’t need a calculator app if you remember two numbers and can multiply. Here is the process broken into five steps.

  1. Identify your ounce type. Is this for cooking (avoirdupois) or precious metals (troy)? This one choice determines everything that follows.
  2. Choose your conversion factor. For avoirdupois: 28.3495. For troy: 31.1035. Rounding to four decimals is fine for most practical purposes.
  3. Multiply ounces × conversion factor. Example: 4 avoirdupois oz × 28.3495 = 113.398g. Example: 1 troy oz × 31.1035 = 31.1035g.
  4. For reverse conversion (grams to ounces): Divide by the same factor. 100g ÷ 28.3495 = 3.527 avoirdupois oz. 100g ÷ 31.1035 = 3.215 troy oz.
  5. Check your scale’s unit setting. If your digital scale can switch between oz and grams, confirm it’s displaying the right ounce system before you weigh.
What to watch

Most consumer scales sold in the US default to avoirdupois ounces. If you’re weighing gold, a jeweler’s scale or a dedicated precious-metals scale will typically read in troy ounces — but always verify the unit setting first.

Upsides and Downsides

Upsides

  • Two distinct ounce systems serve specific purposes — avoirdupois for everyday trade, troy for precious metals
  • Gold’s troy-based pricing is globally standardized, making international comparisons straightforward
  • The 10% difference is consistent and well-documented across multiple authoritative sources

Downsides

  • Confusion between ounce types leads to underpayment when selling gold or overpayment when buying
  • Kitchen scales can’t accurately weigh precious metals — they’re built for avoirdupois ounces only
  • The troy pound being lighter than the avoirdupois pound is counterintuitive and causes errors

Expert Perspectives

The Calculator Site (Conversion Reference)

One ounce (oz) is equal to 28.34952312 grams.

Only Gold (Bullion Specialist)

A standard ounce equals only 28.35 grams, making the troy ounce approximately 10% heavier.

Both references agree on the avoirdupois-to-gram ratio, and together they illustrate why the 10% gap between ounce types matters in practical measurement contexts.

Related reading: 1/2 Cup to Grams

Additional sources

math.tools

While everyday avoirdupois ounces equal precisely 28.35 grams, the Troy gold ounce guide for precious metals weighs 31.1 grams with dedicated conversion tables.

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Frequently asked questions

What is 4 oz to grams?

4 avoirdupois oz = 113.40g. 4 troy oz = 124.41g. The troy measurement is nearly 11 grams heavier.

How many grams in ½ oz?

½ avoirdupois oz = 14.17g. ½ troy oz = 15.55g.

What is 5 oz to grams?

5 avoirdupois oz = 141.75g. 5 troy oz = 155.52g.

How to use 1 oz to grams calculator?

Enter your number of ounces, select either avoirdupois or troy, and multiply by 28.3495 or 31.1035 respectively. Most online calculators auto-detect the unit type, but always confirm which system the tool uses before trusting the result.

What is 10 oz to grams?

10 avoirdupois oz = 283.50g. 10 troy oz = 311.03g.

Is 1 oz gold price per 31 grams?

Yes — gold is priced per 31.1034768 grams (one troy ounce). This is the global standard for all bullion markets.

What metal is 30 times rarer than gold?

Rhodium and osmium are among the rarest precious metals. Rhodium spot prices often reflect its scarcity compared to gold, though rarity rankings shift based on annual mine production data.

For gold buyers, the takeaway is straightforward: never trust a weight quote that doesn’t specify troy ounces. A jeweler or dealer who gives you a price per “ounce” without clarifying which system is either confused or hoping you are. Verify the weight on a scale that displays troy ounces, or walk away.