The formula
Gold value = weight (grams) × purity (carat fraction) × spot price per gram. Purity by carat is fixed: 9ct = 0.375, 14ct = 0.585, 18ct = 0.750, 22ct = 0.916, 24ct = 0.999.
So 20g of 9ct gold at a £97/g pure spot is 20 × 0.375 × £97 ≈ £728 of gold content. Our gold calculator does this instantly against the live London price.
How to check the weight and carat
Weigh your piece in grams on a kitchen or jewellery scale. For mixed pieces, remove stones if you can. You pay for gold content, not the gemstones, in a scrap valuation.
Find the carat from the hallmark stamped on the piece: 375, 585, 750, 916 or 999 correspond to 9ct, 14ct, 18ct, 22ct and 24ct. No hallmark doesn't mean it's fake, but it should be tested.
Scrap value vs what you'll be paid
Scrap (or 'melt') value is the pure metal content at spot. A buyer's offer is that melt value less a commission. At Redisco a transparent 20%, with every figure shown.
Branded, antique or stone-set pieces are valued above melt, because the maker, craftsmanship and gemstones add worth a scale can't see. That's where an AI-plus-gemmologist valuation beats a pure weigh-in.
Where the price comes from
Gold trades globally and is referenced in the UK to the London (LBMA) price, which moves throughout the day. As of mid-2026 the pure (24ct) gold price sat near £97 per gram, after a high of about £107 earlier in June.
Because the price moves, a good valuation locks your offer for a short window so a market dip doesn't catch you out.