The price source
Spot prices come from gold-api.com's free published feed, retrieved every twenty minutes by
our own price service at
https://websites-backend.marava.tech/karatmelt and baked into every page when the site is built. That is why a
figure is on screen before any JavaScript runs, and why the page is correct and indexable with
scripting switched off. When the page loads, the same figures are refreshed from the service so
a cached page cannot show you a stale number without saying so.
Every page prints the date its price belongs to. The gold figures on this build are from . If the service is unreachable at build time, the site falls back to a committed snapshot rather than shipping a blank, and the date on screen will show that the number is old.
The formulas
Melt value of a plain item:
grams = weight x unitGrams x quantity
fineGrams = grams x purityFraction
meltValue = fineGrams x (spotPerTroyOz / 31.1034768)Price of one unit of metal at a purity, which is what the price tables show:
pricePerUnit = (spotPerTroyOz / 31.1034768) x unitGrams x purityFractionGold-filled and rolled gold, where the layer is a fraction of the total weight:
layerGrams = grams x layerFraction
fineGrams = layerGrams x karatFractionA coin, from its mint specification:
fineTroyOz = (coinGrams x fineness) / 31.1034768
meltValue = fineTroyOz x spotPerTroyOzUS 90% silver coin by face value, the way the trade quotes it:
fineTroyOz = faceUsd x 0.715 (circulated)
fineTroyOz = faceUsd x 0.7234 (as struck)Unit constants
| Unit | Grams |
|---|---|
| grams | 1 |
| pennyweight | 1.55517384 |
| troy ounces | 31.1034768 |
| ounces | 28.349523125 |
| kilograms | 1000 |
| grains | 0.06479891 |
A troy ounce is 31.1034768 grams by definition, and every conversion on the site uses that full precision rather than 31.1.
Purity fractions
Karat gold is treated as k divided by 24 exactly, so 14k is 0.583333 rather than the European 585 standard of 0.585. That is the United States legal minimum for a 14k stamp and it is the conservative choice: a figure that is a fraction low is honest, a figure that is high sets you up for disappointment. The difference between the two conventions is 0.29%.
| Metal | Standard | Stamp | Fraction |
|---|---|---|---|
| gold | 24k | 999 | 0.9990 |
| gold | 22k | 916 | 0.9167 |
| gold | 21k | 875 | 0.8750 |
| gold | 20k | 833 | 0.8333 |
| gold | 18k | 750 | 0.7500 |
| gold | 14k | 585 | 0.5833 |
| gold | 12k | 500 | 0.5000 |
| gold | 10k | 417 | 0.4167 |
| gold | 9k | 375 | 0.3750 |
| gold | 8k | 333 | 0.3333 |
| silver | fine silver | 999 | 0.9990 |
| silver | Britannia | 958 | 0.9580 |
| silver | sterling | 925 | 0.9250 |
| silver | coin silver | 900 | 0.9000 |
| silver | European | 800 | 0.8000 |
| silver | 40% clad | 400 | 0.4000 |
| platinum | pure | 999 | 0.9990 |
| platinum | Plat 950 | 950 | 0.9500 |
| platinum | Plat 900 | 900 | 0.9000 |
| platinum | Plat 850 | 850 | 0.8500 |
| palladium | pure | 999 | 0.9990 |
| palladium | Pall 950 | 950 | 0.9500 |
| palladium | Pall 500 | 500 | 0.5000 |
Coin specifications
Coin weights and finenesses are United States Mint specifications, which are public domain
facts rather than anybody data. Actual silver weight is derived from them here rather than
hard-coded, so the arithmetic is checkable:
asw = grams x fineness / 31.1034768. The circulated face value figure of
0.715 troy ounces per dollar, against
0.7234 as struck, reflects roughly 1% of weight lost to wear on
coins that spent decades in circulation. Dealers pay on the circulated figure.
Payout bands
| Buyer | Share of melt |
|---|---|
| a pawn shop | 50% to 60% |
| a local jeweller | 65% to 75% |
| a cash-for-gold buyer | 55% to 70% |
| a mail-in refiner | 80% to 85% |
These are the softest numbers on the site and they are labelled as estimates everywhere they appear. They are trade ranges rather than quotes, they move with lot size and with the refining market, and a particular offer may sit outside them. What buyers actually pay explains where each band comes from. If you have evidence they should move, write in.
Rounding and testing
Nothing is rounded until display, and display is to cents for currency and to a tenth of a gram for weight. The calculation engine is a single module with its own test suite covering the unit conversions, the purity arithmetic, the coin derivations and the face value figures, so the tables, the calculator and the prose on every page are all reading from one implementation and cannot drift apart.
If you find a figure on this site you cannot reproduce from the constants above, that is a bug and we want to hear about it. Email hello@karatmelt.com.
Method questions
Where do your prices come from?
A free published spot price feed (gold-api.com), fetched once for the whole site by our own price service and baked into every page at build time, then refreshed in your browser when the page loads. No dealer feed is involved, because a dealer has an interest in the number.
How often do the prices update?
Each trading day, when the benchmark is published. Every page also carries the date its figures belong to, so you can always see how current the number on screen is.
Why is your 14k figure slightly lower than another calculator?
Because we use 14/24, which is 0.58333, the US legal minimum for the stamp. Some calculators use the European 585 standard, which alloys marginally richer. The difference is under a third of a percent, and we choose the conservative direction deliberately.
Are the payout percentages a quote?
No. They are observable trade ranges, published here so you can see them rather than discover them at a counter. No buyer is bound by them and a particular offer may fall outside.
Do you round the results?
Only for display, to cents. Every calculation runs at full floating point precision underneath, and no intermediate result is rounded before the final one.
Is the calculation done on my device or on your server?
Both, and identically. The page is rendered on the server with a baked price so it works without JavaScript, then the same formula runs in your browser against the live price. If the two ever disagreed, it would be a bug.
Can I check your arithmetic?
That is what this page is for. Every constant and every formula used anywhere on the site is written out below. Take your weight, the purity fraction and the benchmark price, and you can reproduce any figure we print with a pocket calculator.