How to Calculate Gold Value
How to calculate gold value from weight, purity, and spot price — worked gram and DWT examples, karat fractions, and mistakes that skew scrap estimates.
Someone drops a bag of scrap on the counter and asks what it’s worth. If you guess from “feel,” you’ll either insult a seller or overpay a tray that was mostly 10K and solder.
The math isn’t mystical. It’s weight, purity, and a gold price on the same unit basis. Miss one of those—or mix grams with troy ounces—and the number lies with confidence.
This walkthrough shows the formula, karat fractions, worked examples, and the shop mistakes that warp estimates before any buyer opens their mouth.
You’ll get the melt-style method shops use to sanity-check offers, plus how that number differs from cash tickets and refining settlements.
The formula (and what it is not)
Gold value (melt-style estimate) ≈ weight × purity × gold price
All three pieces must share a unit basis. If spot is per troy ounce, convert weight to troy ounces—or convert spot to per gram / per DWT—before you multiply.
This is not a promise of what a pawn ticket, jewelry buy desk, or refiner will pay. Offers often sit below full melt-style value after testing, risk, and margin. For the three-way split, read scrap vs melt vs resale.
If you want a tool that surfaces these inputs instead of hiding them, start with how to choose a scrap gold calculator.
Step 1: Get a clean weight
Zero the scale. Wipe the pan. Note the unit on the ticket before you write a number.
Remove loose stones and clip-on parts when you can. A CZ still in a head is dead weight in the scrap math. If you can’t pull it, estimate the non-gold mass and subtract—or accept a softer estimate.
Mixed karat? Weigh separately. One blended weigh-in hides how much low-karat metal is in the bag.
For filings and sweeps, weight alone is a weak story—contamination is the norm. See bench filings gold value before you treat dust like chain.
Step 2: Convert purity from karat or stamp
Karat is parts gold out of 24:
| Karat | Approx. purity | Common stamp |
|---|---|---|
| 10K | 10/24 ≈ 41.7% | 417 |
| 14K | 14/24 ≈ 58.3% | 585 |
| 18K | 18/24 ≈ 75.0% | 750 |
| 21K | 21/24 ≈ 87.5% | 875 |
| 22K | 22/24 ≈ 91.7% | 916 |
| 24K | ≈ 99.9% | 999 |
Keep the gold purity and hallmark chart and what gold hallmark numbers mean nearby when stamps are worn or foreign.
If the piece looks soft for its mark—or is stamped half-karat under—don’t force the optimistic fraction. Details live in half karat under plumb.
Step 3: Put price on the same unit
Troy ounce is the usual wholesale quote. Shop work often needs per gram or per DWT.
Useful conversions:
- 1 troy ounce = 31.1035 g
- 1 DWT = 1/20 troy ounce ≈ 1.55517 g
So if EXAMPLE spot = $2,400 / troy oz:
- Per gram ≈ 2400 ÷ 31.1035 ≈ $77.16 / g
- Per DWT ≈ 2400 ÷ 20 = $120.00 / DWT
Full unit deep-dive: pennyweight vs grams vs troy ounce.
Label every example price as illustrative unless you’re locking a live quote for that ticket.
Worked example A — grams and 14K
Weight: 15.0 g stamped 14K, no stones.
Purity ≈ 0.583
EXAMPLE spot: $2,400 / troy oz → ≈ $77.16 / g
Fine gold mass ≈ 15.0 × 0.583 = 8.745 g
Estimate ≈ 8.745 × 77.16 ≈ $675
That’s melt-style math. A walk-in offer can land lower. A refining settlement adds fees and accountability terms—see accountability vs treatment charge.
Worked example B — DWT and 18K
Weight: 10.0 DWT of 18K.
Purity ≈ 0.750
EXAMPLE spot: $2,400 / troy oz → $120 / DWT for pure gold
Fine gold in DWT ≈ 10.0 × 0.750 = 7.5 DWT
Estimate ≈ 7.5 × 120 = $900
Same formula. Different unit. Don’t multiply gram weight by a per-DWT price.
Common mistakes that warp the number
Unit collision. Entering grams while the price basis is per troy ounce without converting. Fix the basis first.
Stones and steel. Clasps, spring rings, and watch backs sneak into “gold weight.”
Gold-filled as solid. Filled and plated are not 14K solid math. Recoverable gold is a thin layer story.
One karat for a mixed tray. Separate lines beat a fantasy average.
Under-plumb ignored. Stamped 14K that assays soft needs a lower purity input.
Treating estimate as settlement. Melt-style value is a ceiling for conversation, not a wire amount. Packing and lot notes still matter when you send scrap for refining.
Quick checklist before you quote
- Unit written on the ticket (g / DWT / troy oz).
- Karat or millesimal written next to weight.
- Stones / hardware called out or removed.
- Spot source and timestamp (or “example”) noted.
- Separate lines for separate karats.
- Language: “estimate,” not “guaranteed payout.”
Keep exploring
- Goldcalculator
- gold value calculator
- gold melt calculator
- all gold calculators
- gold purity hallmark chart
- pennyweight vs grams vs troy ounce
- half karat under plumb
Frequently Asked Questions
Is karat purity exact enough for a buy ticket?
Karat fractions are standard shop math. Final settlement still depends on testing or assay. Use karat for estimates; don’t pretend a stamp replaces a melt assay on big lots.
Should I use today’s spot or yesterday’s close?
Use the price basis that matches how the deal settles. If the buyer locks a quote, write that number on the ticket. Stale spot is how desks over-promise.
How do I handle jewelry marked 585?
585 means about 58.5% gold—treat it like 14K-class purity. Enter millesimal if the tool allows, or use ~0.585 in the formula.
Why is my estimate higher than every offer I get?
Because offers bake in testing risk, overhead, and margin. Melt-style math is a reference line. Comparing offers to that line is useful; expecting every buyer to meet it is not.
Can I calculate value without a scale?
Not responsibly. Weight is half the story. Borrow or buy a scale that reads to at least 0.1 g for jewelry scrap; finer for small lots.
Do dental gold and coin gold use the same formula?
Same structure: weight × purity × price. Dental alloys and coin compositions vary—confirm purity before you apply jewelry karat tables blindly.
What’s the fastest way to sanity-check a calculator result?
Recreate one line by hand: convert units, apply purity, multiply. If you can’t match the screen within rounding, don’t trust the screen.
Next step
Take one real piece from the tray, weigh it, write unit and karat on paper, and run the formula with today’s spot labeled clearly. Then compare that estimate to the last offer you accepted—and note where packing or refining terms would change the story after the math.