Gold Karat Calculator – Purity & Melt Value

Karat is the grade. Purity is the fraction. Dollars need both—plus weight and a spot basis. Mix those up and you’ll grade a tray wrong before the first offer arrives.

Stamps help when they’re real. 585 and 14K point at the same neighborhood. Worn marks, English conventions, and under-plumb habits still bite.

This gold karat calculator converts karat ↔ purity and runs a melt-style estimate once you’ve weighed the metal, so grading and pricing stay on the same page.

Karat to purity (the only conversion that matters)

Purity ≈ karat ÷ 24

Karat	Purity (approx.)	Common number stamp
10K	41.7%	417
14K	58.3%	585
18K	75%	750
21K	87.5%	875
22K	91.7%	916
24K	99.9%	999

Full chart energy lives on the gold purity hallmark chart. Number-stamp stories: gold hallmark numbers meaning.

How to grade, then price

Find every stamp you can — Loupe the insides and clasp tags.
Map stamp → karat — 750 means 18K territory, not “maybe 14.”
Test when unmarked or suspicious — Color is not a grade.
Weigh by karat group — Grading fails if 10K and 18K share one bag.
Calculate — Purity × weight × spot in this tool.
Flag under-plumb suspects — Older goods may assay light of stamp; read half karat under plumb.

Hallmarks aren’t decoration

A stamp is a claim. Refiners pay on assay. Cash buyers often pay on the lesser of stamp and what their test says.

If you grade everything “14K average,” you donate the 18K upside and overcredit the 10K. Karat discipline is free money on mixed estates.

Gold-filled marks (1/20 14K GF) are not solid karat grades—send those to the gold filled calculator.

Worked EXAMPLE

EXAMPLE spot: $2,400 / troy oz (illustrative).

You graded a bracelet as 18K (purity 0.75) at 15 g net.

Fine grams ≈ 15 × 0.75 = 11.25 g.
Fine oz ≈ 11.25 ÷ 31.1035 ≈ 0.362 oz.
Illustrative melt-style ≈ 0.362 × $2,400 ≈ $869.

Mis-grade that same bracelet as 14K and you’d print ≈ 15 × 0.583 × (2400 ÷ 31.1035) ≈ $675. Same metal on the scale—wrong karat tax of roughly $194 in this EXAMPLE. Grade carefully.

From karat grade to selling decisions

Once purity is set, the dollar path still splits: scrap, cash-for-gold, or intact resale. Karat only fixes the metal fraction. Channel choice fixes expectations—see scrap vs melt vs resale.

Dedicated karat pages help when a whole tray is one grade: 10K, 14K, 18K, 22K, 24K.

Grading mistakes that show up on the settlement

Trusting color — Rose and white alloys still follow the stamp. Brass-colored base metal can fool a quick glance.
One bag, many karats — Estate cleanouts love mixing. Sort first or your average grade is fiction.
Paying filled as solid — GF and plate marks get ignored when someone is tired. Separate them before you calculate.
Ignoring solder and repairs — Soft solder joints and replacement clasps can assay differently than the main links. Note repairs on the packing sheet.
Skipping the loupe — Worn 585 can look like a scratch. Take thirty seconds.

If you’re shipping to a refiner, karat grades on your packing list should match what you typed here. When assay comes back light, you’ll know whether the fight is grade, weight, or fees.

Unit mix-ups still wreck good grading. Keep pennyweight vs grams vs troy ounce handy when the buyer’s ticket uses a different scale language than yours.

gold karat calculator gold value tips — Visual guide supporting gold karat calculator — weight, karat, and melt-style estimates.

Related tools and guides

Frequently Asked Questions

How do I calculate gold purity from karat?

Divide karat by 24. 18 ÷ 24 = 0.75.

Is 585 always exactly 14K?

It’s the common millesimal mark for ~14K / 58.5% style purity. Manufacturing tolerances and under-plumb practice still exist.

Can this calculator convert purity back to karat?

Yes—karat ≈ purity × 24. Handy when you only have a decimal assay.

What if two stamps disagree?

Test. Don’t average stamps for fun. Resolve the conflict before you price.

Does higher karat always mean a better sale?

More fine gold per gram, yes. Wear hardness and local demand are separate issues.

Are European hallmarks different?

Number systems and office marks vary by country. Millesimal fineness (e.g., 750) still maps to purity the same way.

Should I grade filings by the jewelry they came from?

Only as a starting guess. Filings pick up dirt and mixed alloys—assay is safer. See bench filings gold value.

Disclaimer

Karat conversions and EXAMPLE valuations are educational estimates. Stamps can be wrong; assays govern settlement. This is not refining or legal advice.