Gold Weight Calculator

18 karat gold means the alloy contains 18 parts pure gold out of 24 total parts, giving it a fineness of 0.750 or 75% pure gold. The remaining 25% consists of other metals like copper, silver, or zinc added to improve durability. 18K gold is one of the most common grades used in fine jewelry.

Gold fineness expresses purity as parts per thousand — for example, 18K gold has a fineness of 750, meaning 750 out of 1000 parts are pure gold. Karat is a related but older system measured out of 24 parts. Both describe purity: 24K = fineness 999, 18K = 750, 14K = 583, and so on.

To calculate gold weight, you need the physical dimensions of the piece (length, width, thickness) and the density of your specific gold alloy. Multiply volume by density to get total mass, then multiply by the fineness (karat ÷ 24) to find the pure gold content. Our calculator handles the purity math once you enter your measured weight.

The karat value can be found with the formula K = 24 × (mass of pure gold / total mass of the alloy). If you know the total weight and have tested the purity content, divide the pure gold mass by total mass and multiply by 24. Most jewelry is stamped with its karat value, or you can use a gold testing kit.

The value of gold per gram depends on the current spot price per troy ounce and the karat purity of the piece. Since 1 troy ounce equals 31.1035 grams, divide the spot price by 31.1035 to get the per-gram price, then multiply by the fineness ratio. For example, at $2300/troy oz, pure 24K gold is worth roughly $73.94 per gram, while 18K gold would be about $55.45 per gram.

A pennyweight (abbreviated DWT) is a unit of weight used in the precious metals and jewelry trade. One pennyweight equals 1.55517 grams, and there are 20 pennyweights in one troy ounce. Some jewelers and scrap gold buyers quote prices in DWT, so it's useful to be able to convert between units.

A price spread (or dealer discount) is the difference between the spot market price of gold and the lower price a buyer actually pays for scrap or used gold. Dealers apply a spread to cover processing costs and profit margin. A 10% spread on $2300/oz spot means you'd receive $2070/oz equivalent. Enter your dealer's spread percentage in the calculator to see your realistic payout.

A digital gram scale accurate to at least 0.1 grams is recommended for weighing gold at home. Dedicated jewelry scales that read to 0.01 grams offer even greater accuracy. Standard kitchen scales can give a rough estimate but may not be precise enough for small pieces. Affordable digital scales are widely available online for under $15.