The detailed guide below is currently available in English.
Troy weight and regional units
Precious metals ignore kitchen scales. The trade unit is the troy ounce of 31.1034768 grams — about 9.7% heavier than the everyday (avoirdupois) ounce — and there are only twelve to the troy pound. Regional units persist too: Indian jewelry is quoted in tolas of 11.6638038 g, and Thai gold shops sell by the baht of 15.244 g. Mixing these up is the classic buying mistake, so this calculator converts everything to grams and troy ounces before any valuation.
How purity turns weight into value
A karat is a 24th, so 18K jewelry is 18/24 gold — but traders use the millesimal stamp instead: 999 (24K), 916 (22K), 750 (18K), 585 (14K). Only the fine content counts at spot price, so a 10 g baht-weight 22K chain holds 15.244 × 0.916 ≈ 13.96 g of pure gold. The remainder is the alloy that hardens the metal, and it is worth nothing at the refiner. Coin and bar buyers should note that bullion carries premiums above spot, while scrap sellers receive a percentage below it.
Repères pour la France
Repères locaux pour la France, utiles dans les calculs du quotidien :
- TVA: 20 % en taux normal (5,5 % alimentaire, 10 % restauration) ; les prix sont TTC par loi.
- Monnaie & paiements: Euro (€) ; paiement sans contact et carte bancaire très répandus, virement SEPA instantané en développement.
- Unités & nombres: Système métrique ; virgule décimale et espace pour les milliers : 1 234,56 €.
- Santé: Carte Vitale ; l'Assurance Maladie rembourse en base ≈ 70 % des soins, le reste par mutuelle.
- Pourboire: Service compris : aucun pourboire obligatoire ; arrondir suffit.
Mis à jour : octobre 2026 · valeurs 2025, sources officielles ci-dessus.
Questions fréquentes
Why is a troy ounce different from a regular ounce?
The troy system is a medieval trading standard kept for precious metals: one troy ounce is 31.1034768 grams versus about 28.35 for a grocery-store ounce. Gold, silver, platinum, and gunpowder all use it, and no other commodity does.
What does 916 mean on my jewelry?
It is parts of pure gold per thousand — 916 fine, the millesimal way of writing 22K. The same logic gives 999 for 24K, 750 for 18K, and 585 for 14K. The calculator uses these fractions to extract the fine gold from the gross weight.
Will a dealer actually pay this spot value?
Treat the figure as the midpoint of negotiation. Refiners and jewelers buy scrap at a discount to cover assaying and refining, typically a few to fifteen percent, while coins and bars sell at a premium over spot. Check the live price at the moment of the deal, because it changes minute to minute.