Method: how this site works

One engine, the same as the app

The calculator and the stamp search on this site run the same engine file as the Pennyweight iPhone app. It loads in your browser (version 1.0.0-motor.1, build 631653dac473) and does the sums and the readings there. No result is computed on a server and none is reimplemented in the page: the page only passes it what you typed and displays what it returns.

The sum

Melt value = (weight − weight that is not metal) × fineness ÷ 1000 × spot price per gram. The price per gram is the price per troy ounce divided by 31.1034768. One pennyweight is 1.55517384 g (1/20 oz t). The scale accuracy you give adds a low-high range. The sum is deterministic: the same inputs always give the same result.

The tables

• 33 fineness standards (gold, silver, platinum, palladium), each with where it is legal. 28 are checked against a statute or convention text; the rest are marked as arithmetic or trade usage on their pages.
• 58 stamps and symbols with a page each: fineness numbers and karat forms, gold filled, rolled and plated stamps, alloys without precious metal, UK hallmark symbols and the French and Vienna Convention marks.
• Date letters for 6 UK assay offices, with every cycle, its letters and styles and the month the letter changes. Unified cycles from 1975.
• 80 construction features with not-before dates and typical years; 39 are marked as verified against their cited reference; the others rest on a single secondary reference and the page says so.
• 13 material look-alike entries, with the rules on ivory, tortoiseshell and coral.

Every page lists its sources. All sources.

What it says, and how firmly

A stamp is a statement by the maker, not proof. The tool says what a stamp claims, never that a piece is genuine. Wording on the site follows that: “stamped” and “marked”, not “is gold”. For plated, filled and rolled stamps it does not compute a melt value.

What it cannot know

• Whether a stamp is genuine, or was struck on a plated piece. Only an assay (touchstone and acids, or X-ray fluorescence) settles that.
• What a stone is, or what it is worth.
• What a buyer will pay. Dealers and refiners deduct a margin, so melt value is a ceiling for scrap, not a quote.
• Anything about age, maker, design or provenance, which can make a piece worth far more than its metal.

Prices

This site never loads a price. The number pre-filled in the calculator is an example, taken from a snapshot of 2026-11-10 (api.gold-api.com), marked as an example wherever it appears. Replace it with today's spot price from a source you trust.

Corrections

If you find a mistake, write to pennyweight@joseluissaorin.com with the page and the source. Tables are regenerated from the engine, so a fix reaches every page.