A troy ounce is heavier than the ounce on your kitchen scale — by about 10%. Get that wrong and every gold figure you calculate is off by a tenth.
You put Grandma’s gold chain on the kitchen scale, it reads one ounce, you multiply by the gold price you saw online — and you’ve just overestimated it by about 10%. Not because the scale is broken. Because it’s weighing the wrong kind of ounce.
This is the single most common unit mistake in precious metals, and it costs people real money in both directions. Understanding troy ounce vs. ounce takes about two minutes, and once you’ve got it, none of the numbers can trip you up again. Let’s clear it up.
The 10% mistake in one line
There are two different “ounces,” and they are not the same weight:
A troy ounce (the metals ounce) is 31.1035 g. A regular ounce (the kitchen ounce) is 28.3495 g.
The troy ounce is heavier — by about 9.7%, call it a tenth. Gold, silver, platinum and palladium are always priced per troy ounce. So if you weigh a piece as “one ounce” on a food scale (28.35 g) and multiply by a price that’s quoted per troy ounce (31.10 g), you’ve mixed two units and your answer is off by roughly 10%.
The fix is boringly simple: work in grams. Grams are grams everywhere — no troy-versus-not confusion — and gold has a clean per-gram price. That’s exactly how the melt-value calculator works, so you never touch an ounce at all.
Why two ounces even exist
The “regular” ounce has a proper name: the avoirdupois ounce. It’s the one baked into food scales, postal scales and bathroom scales across the English- speaking world — 28.3495 g, sixteen to the pound.
The troy ounce is older and narrower. It survived as the dedicated unit for precious metals and gemstones, and the global bullion market never gave it up. The LBMA benchmark, COMEX futures, refiners’ payout sheets — all of it is quoted and settled in troy ounces. Keeping one unit means a price in London, New York and Dubai all mean the same thing.
The conversion table you can trust
Here are the units that actually matter for precious metals, all pinned to grams. These figures are fixed by definition — they don’t change with the market:
| Unit | Symbol | Grams | Relationship |
|---|---|---|---|
| Gram | g | 1 | the base unit |
| Troy ounce | ozt | 31.1035 | 20 dwt · 480 grains |
| Pennyweight | dwt | 1.55517 | 1/20 troy ounce |
| Grain | gr | 0.06480 | 1/480 troy ounce |
| Avoirdupois ounce | oz | 28.3495 | the kitchen ounce |
Two of these deserve a word. The pennyweight (dwt) is the unit many pawn shops and scrap buyers weigh in — 20 dwt make one troy ounce. If a buyer quotes you a price “per pennyweight,” they’re quoting per 1.55517 g, and it’s worth converting so you can compare apples to apples. The grain is the tiny unit used in assay and for very small quantities: 480 grains to the troy ounce, 24 to the pennyweight.
The world’s other gold units
Precious metals are global, and several traditional units are still in daily use. The GramValue calculator supports the main ones, because a chain bought in Mumbai or Bangkok is often described in local units:
| Unit | Region | Grams (approx.) |
|---|---|---|
| Tola | India / Pakistan | 11.6638 |
| Baht | Thailand (bullion) | 15.244 |
| Tael | Hong Kong / SE Asia | ~37.8 |
The tola is precise and well-standardised: 11.6638 g, which is exactly 180 troy grains. The baht is the Thai gold unit; bullion is 15.244 g per baht, though Thai jewelers often use a slightly lighter 15.16 g for finished pieces.
The tael is the one to be careful with — it genuinely varies by region. The Hong Kong / Southeast-Asian jewelry tael is about 37.8 g (the value the calculator uses), the Taiwan tael is 37.5 g, and the mainland-China market tael is a round 50 g. If someone quotes a tael, ask which one they mean before you do any math.
Weighing it right
Once you’re working in grams, the only thing left is a trustworthy weight. This is where a bit of cheap kit earns its place — and where I’ll be upfront that the links below are affiliate links.
You want a scale that reads to 0.01 g. A whole-gram kitchen scale rounds away real value on a light earring or a thin chain, and it can’t show you the fractions that matter. A a 0.01 g digital jewelry scale that also switches to troy ounces and pennyweight lets you weigh in grams and still read a buyer’s dwt quote in their own units.
The catch nobody mentions: every small scale drifts. Temperature, a knock in the drawer, an aging sensor — over time the reading wanders. That’s why scales have a calibration mode and a spot for a reference weight. A a 100 g calibration weight lets you confirm the scale is honest in ten seconds: place it, check it reads 100.00 g, and you know the weight under your gold is real.
Putting it together
Say you’ve got a gold chain and your 0.01 g scale reads 12.4 g. You don’t need to touch ounces at all:
- Weight: 12.4 g — already in grams, no conversion.
- Purity: read the hallmark — say it’s 14K, so 58.5% pure gold.
- Value: 12.4 g × 0.585 × the live per-gram gold price. The gold calculator fills in that last number live, so nothing goes stale.
Compare that to the trap: weigh it as “0.4 oz” on a food scale, treat that as troy ounces, and you’d feed a wrong unit into every step. Grams keep you honest.
Curious how the pieces fit into a full valuation? Our how much your gold jewelry is worth guide walks the entire calculation, and the six-step selling guide covers comparing offers without getting talked down.
So: troy ounce vs. ounce. One is 31.1035 g, the other 28.3495 g, and mixing them is a 10% error. Weigh in grams, keep a calibration weight in the drawer, and let the calculator handle the conversions — that’s the whole trick to never being off by a tenth again.
Common questions
What is the difference between a troy ounce and a regular ounce?
A troy ounce weighs 31.1035 grams; a regular (avoirdupois) ounce — the one your kitchen scale uses — weighs 28.3495 grams. The troy ounce is about 9.7% heavier, roughly a tenth. Precious metals are always priced per troy ounce, so if you weigh gold in regular ounces and multiply by a per-troy-ounce price, your figure comes out about 10% too high.
How many grams are in a troy ounce?
One troy ounce is 31.1035 grams (31.1034768 g to be exact). That is the unit gold, silver, platinum and palladium are quoted in worldwide. A kitchen ounce, by contrast, is 28.3495 grams.
Why is gold weighed in troy ounces?
It is a historical convention that stuck. The troy system was standardised for precious metals and gemstones centuries ago, and the global bullion market — LBMA, COMEX, refiners — still quotes and settles in troy ounces. Using one consistent unit keeps prices comparable everywhere, even though almost everyone now weighs the metal itself in grams.
What is a pennyweight (dwt)?
A pennyweight is a small troy unit still used in the jewelry and scrap trade. One pennyweight is 1.55517 grams, and there are exactly 20 pennyweights in a troy ounce. Some buyers quote scrap prices per pennyweight, so it pays to know the conversion before you sell.
Can I use my kitchen scale to weigh gold?
Only for the roughest guess. Most kitchen scales read in whole grams and drift out of calibration, which rounds away real money on a light chain. For anything you plan to sell, use a scale that reads to 0.01 g and check it against a known calibration weight.
How do I convert grams to troy ounces?
Divide the weight in grams by 31.1035. For example, 10 grams ÷ 31.1035 = 0.3215 troy ounces. To go the other way, multiply troy ounces by 31.1035. The GramValue calculator does the conversion for you and applies the live per-gram price in the same step.