GOLD UNIT FOUNDATIONS · 11 MIN READ
Troy ounce vs. regular ounce
A troy ounce is 31.1034768 grams. A regular household ounce, formally called an avoirdupois ounce, is 28.349523125 grams. The troy ounce is therefore 2.753953675 grams, or about 9.714%, heavier. Gold, silver, platinum and palladium prices normally use troy ounces. Using an ordinary ounce in a precious-metal calculation will misstate the weight and price per gram.
The standard ounce used for precious metals.
The avoirdupois ounce used for most everyday goods.
One troy ounce contains more mass.
Troy ounce compared with the regular ounce.
INTERACTIVE UNIT WORKBENCH
Convert troy, ordinary, metric and regional gold weights
Select the exact source and destination units. The converter passes every conversion through an explicit grams-per-unit constant and keeps troy ounces separate from ordinary ounces. Optional purity and live-price inputs can calculate contained gold and metal value.
Price reference
Shows the source and observation time of the metal price used here. Product premiums, dealer quotes and taxes are separate.
- Source
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- Observed
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- Age
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- Delivery
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Checking the current market reference.
Apply fineness after converting mass
Weight conversion does not change purity. Enter the item's fineness to calculate contained gold and a live metal reference.
One input across all supported units
| Unit | Equivalent | Grams per unit | Definition |
|---|---|---|---|
| MilligramMetric · mg | 31,103.4768 mg | 0.001 g | One thousandth of a gram. |
| GramMetric · g | 31.1034768 g | 1 g | SI metric reference unit used by this calculator. |
| KilogramMetric · kg | 0.0311034768 kg | 1,000 g | 1,000 grams. |
| GrainTroy · gr | 480 gr | 0.06479891 g | 1/480 of a troy ounce. |
| PennyweightTroy · dwt | 20 dwt | 1.55517384 g | 24 grains or 1/20 troy ounce. |
| Troy ounceTroy · oz t | 1 oz t | 31.1034768 g | Precious-metals ounce; not the ordinary ounce. |
| Troy poundTroy · lb t | 0.083333333333 lb t | 373.2417216 g | 12 troy ounces. |
| Ordinary ounce (avoirdupois)Avoirdupois · oz av | 1.0971428571 oz av | 28.349523125 g | The common household ounce; not a troy ounce. |
| Ordinary pound (avoirdupois)Avoirdupois · lb av | 0.068571428571 lb av | 453.59237 g | 16 ordinary ounces. |
| TolaSouth Asia · tola | 2.6666666667 tola | 11.6638038 g | Reference convention: 3/8 troy ounce. |
| Vori / BhoriSouth Asia · vori | 2.6666666667 vori | 11.6638038 g | Bangladesh market name using the calculator's tola-equivalent convention. |
| Hong Kong troy taelEast Asia · HK tael | 0.830999406877 HK tael | 37.429 g | Hong Kong precious-metals troy tael. |
| Hong Kong troy maceEast Asia · HK mace | 8.3099940688 HK mace | 3.7429 g | 1/10 Hong Kong troy tael. |
| Taiwan taelEast Asia · TW tael | 0.829426048 TW tael | 37.5 g | Regional 37.5-gram convention; do not substitute for Hong Kong tael. |
| Thai baht weight — bullionThailand · baht bar | 2.0403750197 baht bar | 15.244 g | Thai gold-bar weight reference. |
| Thai baht weight — jewelryThailand · baht jewelry | 2.0516805277 baht jewelry | 15.16 g | Thai gold-jewelry weight reference; differs from bullion. |
A calculated match does not verify a scale, hallmark, fineness or product. For a material transaction, confirm the unit convention printed on the quote and use a suitable calibrated scale.
SIDE-BY-SIDE
The two ounce systems are not interchangeable
PRICE CALCULATION
Why the wrong ounce creates a 9.714% price error
Apply a purity factor afterward when the object is not pure gold.
This is the precious-metal quote convention.
$2,400 ÷ 31.1034768 equals about $77.16 per gram.
$2,400 ÷ 28.349523125 incorrectly produces about $84.66 per gram.
The incorrect result overstates the pure-gold price per gram by about 9.714%.
THE TWO POUNDS TRAP
A troy ounce is heavier, but a troy pound is lighter
The result sounds contradictory until the number of ounces per pound is included. A troy pound contains 12 troy ounces and weighs 373.2417216 grams. An avoirdupois pound contains 16 ordinary ounces and weighs 453.59237 grams. The individual troy ounce is heavier, but the troy system uses fewer ounces per pound.
373.2417216 grams.
453.59237 grams.
Identify the weight system first.
Metric mass removes abbreviation ambiguity.
BULLION COINS
“One ounce” can mean fine-gold content, not gross coin weight
The fine-gold weight is the amount of pure gold inside a product. Gross weight includes gold plus any alloy metals. The U.S. Mint’s Gold Eagle specifications state that the one-ounce coin contains one gold troy ounce but weighs 1.0909 troy ounces, or 33.931 grams, because its composition also includes silver and copper. A .9999 fine one-ounce Gold Buffalo is much closer to one troy ounce gross weight because almost the entire coin is gold.
Use official mint specifications when available; do not reconstruct a published fine weight from rounded display values unless necessary.
LABELS AND ABBREVIATIONS
“oz” alone can be ambiguous outside a bullion context
WHY PRECIOUS METALS USE TROY WEIGHT
The convention survives because a shared standard reduces ambiguity
Troy weight has a long commercial history in precious metals. The practical reason it remains important today is standardization: refiners, vaults, exchanges, mints and dealers need a common weight basis. Changing the unit would not change the amount of metal, but mixing systems during a transaction would change the apparent quantity and price.
NIST’s precious-metals guidance notes that precious metals sold by weight should use troy weight or SI units and that conversion information should facilitate price comparison. NIST’s SI conversion appendix lists separate conversion factors for avoirdupois and troy ounces.
BUYING AND SELLING CHECKLIST
How to prevent an ounce mistake in a real quote
01Ask whether “ounce” means troy, avoirdupois or fluid ounce.
02Record the exact gross weight in grams when possible.
03Verify fineness or karat separately from weight.
04Calculate fine-gold weight before applying the market price.
05Compare price per fine gram or fine troy ounce, not package weight.
06Keep premiums, fees, stones and non-gold components outside melt value.
PRIMARY SOURCES & METHOD
Exact constants used by GoldObserve
- NIST Guide to the SI, Appendix B.8 for separate troy and avoirdupois ounce conversion factors.
- NIST precious-metals conversion information for troy or SI sales and comparison guidance.
- U.S. Mint American Gold Eagle specifications for the distinction between fine-gold content and gross coin weight.
- GoldObserve methodology for unit normalization, purity and price calculation order.
GoldObserve stores one troy ounce as 31.1034768 grams and one avoirdupois ounce as 28.349523125 grams. Display values may be rounded, but calculations retain the full constants shown here.
RELATED TOOLS & GUIDES
Continue from weight to purity and value
FAQ
Troy ounce and regular ounce questions
How many grams are in a troy ounce of gold?
One troy ounce equals 31.1034768 grams in the exact conversion convention used by GoldObserve.
Is a troy ounce heavier than a regular ounce?
Yes. A troy ounce is about 9.714% heavier than an ordinary avoirdupois ounce.
Why are gold prices quoted in troy ounces?
Troy weight is the established precious-metals convention, giving wholesale markets, mints, refiners and dealers a shared mass standard.
Does a one-ounce Gold Eagle weigh one troy ounce?
It contains one troy ounce of fine gold but weighs more in total because the coin also contains alloy metals.
Is a fluid ounce related to a troy ounce?
No. A fluid ounce measures volume. Troy and avoirdupois ounces measure mass.