9ct vs 14ct vs 18ct vs 22ct gold: the difference in value per gram

The carat system, plainly

Carat is a measure of purity, nothing more complicated. Pure gold is 24 carats by convention. 18ct gold is 18 parts gold to 6 parts other metal, which works out at 18/24 or 75.0% pure gold. 22ct is 22/24, or 91.7%. 14ct is 14/24, or 58.5%. 9ct is 9/24, or 37.5%. The remaining percentage in any carat is the alloying metals (copper for warmth, silver for paleness, zinc and palladium for various properties) that give the metal strength, colour and workability. Pure gold is too soft to hold a setting or take everyday wear.

The same carat ratios are written two different ways depending on context. Old British hallmarks used the carat number (9ct, 18ct, 22ct). Modern UK hallmarks since 1975 use the millesimal fineness, the purity expressed as parts per thousand: 375 for 9ct, 585 for 14ct, 750 for 18ct, 916 for 22ct, 999 for 24ct. Both numbers describe exactly the same alloy. A ring stamped "375" and a ring stamped "9ct" are the same purity of gold.

A brief history of the UK hallmark

UK hallmarking is one of the oldest forms of consumer protection in the world. Statutory marking of precious metal in London began in 1300 under a statute of Edward I; assaying moved to Goldsmiths' Hall in 1478, and the word "hallmark" comes directly from that building. Four UK assay offices operate today: London (leopard’s head), Birmingham (anchor), Sheffield (rose) and Edinburgh (castle). Any solid gold item above the legal exemption weight, currently 1g for gold, must be hallmarked by one of those four offices before being sold as gold in the UK.

The full hallmark contains three compulsory marks (sponsor, fineness, assay office) and a number of optional ones (date letter, traditional standard mark, commemorative marks). A full walkthrough sits on the hallmark guide and a 60-second reading method on the quick-read blog post. Either is enough to identify a UK piece in a minute or two.

The maths, worked through on a 30g chain

The cleanest way to feel the carat ladder is to work it through on a real lot. Take a single chain weighing 30g (a heavy but realistic curb chain) and run it at every carat. To do this you need a per-gram price for fine gold; the exact number moves intra-day, so take it from a dated public source on the day. The price moves; the structure of the maths does not.

The formula is the same every time: (weight × purity × the day’s price), where purity is the decimal fraction (0.375 for 9ct, 0.916 for 22ct). GoldPaid’s margin is already inside the offer, so nothing further comes off, and it is what funds the labels, the XRF equipment, the chain of custody and the free return.

Two things stand out. First, the spread is wide: the same 30g of metal holds roughly two-and-a-half times more fine gold at 22ct than at 9ct. Second, the fine-gold content is exactly linear in the carat: 18ct holds precisely twice the pure gold of 9ct (75.0 ÷ 37.5 = 2.0), because carat is simply parts of gold in 24. What is not linear is anything else about the piece: the resale premium, the desirability of the colour, the market for the style. For the others the ratios are: 14ct ≈ 1.56× 9ct, 22ct ≈ 2.44× 9ct, 24ct ≈ 2.66× 9ct.

Why 9ct dominates British jewellery boxes

9ct gold is the workhorse of UK jewellery and has been since 1854, when the lower standard was first hallmarked in Britain. There are three reasons it became the British default. First, cost. 9ct uses 37.5% gold rather than 75% or 91.7%, so the same design at 9ct is roughly half the metal cost of the equivalent at 18ct, which puts gold within reach of ordinary household budgets for everyday pieces like wedding bands, chains and signet rings.

Second, durability. 9ct is harder than higher carats because the alloying metals (copper, silver and zinc) provide structural strength that pure gold lacks. A 9ct ring takes daily wear, knocks on door frames and washing-up duty without deforming. An 18ct ring of the same design is noticeably softer; a 22ct ring is softer still. For a piece intended to be worn every day for decades, the lower carat is often the more practical choice.

Third, the British high-street trade. From the late nineteenth century onwards, the UK jewellery industry was structured around 9ct as the volume standard, with 18ct as a premium upgrade and 22ct as a specialist option. That commercial structure is still visible today in any Hatton Garden window. A typical UK jewellery box from a clearance is dominated by 9ct chains, rings and bracelets, with a few 18ct pieces (often engagement and wedding rings) and very little above that.

Why 22ct is the standard in South Asian wedding jewellery

In India, Pakistan, Bangladesh, Sri Lanka and the wider South Asian diaspora, the dominant carat is 22ct, not 9ct or 18ct. The reasons are partly cultural, partly economic and partly historical. Culturally, gold in South Asian tradition is both ornament and store of value, often gifted in significant quantity at weddings; the higher carat is the visible, audible signal of that value, both in deeper yellow colour and in unalloyed weight. Economically, gold has been a more consistent inflation hedge than many local currencies over the last several decades, so families have a genuine interest in jewellery that doubles as savings, which favours higher-purity, lower-craftsmanship pieces (the labour cost of a wedding set is a smaller share of the total than in a 9ct ring, where labour can exceed metal value).

Historically, 22ct (or sometimes 23ct in regional traditions) has been the customary wedding-gold standard across the subcontinent for centuries, predating the British 9ct convention by a long way. UK-based families from these traditions often hold significant 22ct pieces alongside any 9ct everyday jewellery. When such items are sold (a common context is following a death, downsizing or simply a generational change of taste), the value gap with 9ct is real and worth understanding. A 22ct wedding set of 100g is in a different league from a 9ct chain of the same weight: it contains roughly two-and-a-half times the fine gold, so it is worth correspondingly more in metal.

14ct, 21ct and the in-between carats

14ct (585) and 21ct (875) sit in the gaps between the dominant UK and South Asian standards. 14ct is the volume standard in the United States and Germany and is therefore common in jewellery imported from those markets, including a lot of late-twentieth-century American chains and rings. 21ct is associated mainly with Egyptian and Levantine traditions and is rarer in UK estates but does turn up in family collections from those backgrounds. Both are perfectly straightforward at assay: XRF reads the purity to a precise percentage, and the per-gram rate is calculated against the actual fineness rather than rounded to the nearest UK carat.

You will also occasionally see 8ct (333) or 15ct (625). 8ct was used in some German and Austrian pieces; 15ct was a historical British standard used between 1854 and 1932. Both are priced honestly on actual content, never rounded down to 9ct or 14ct simply because they are non-standard.

A second worked example: mixed-lot intuition

A useful intuition for anyone preparing a postal lot is that low carat with high weight roughly equals high carat with low weight. Take a 10g 9ct chain (3.75g of pure gold) and a 5g 18ct ring (3.75g of pure gold). They contain exactly the same fine-gold content, and the two offers will be very close. Where they differ in practice, it is because of the pieces themselves (stones, a base-metal spring, a hollow section), not because of the carat. GoldPaid’s method is to price the tested purity against the live precious-metal market and multiply by the payable weight, with no fixed fee added or deducted.

This is also why a buyer who weighs and assays mixed lots properly will always separate by carat first. A 30 g mixed lot of 20 g 9ct and 10 g 18ct holds 15 g of fine gold, which is arithmetically the same as 30 g of 12ct, so a correctly weighted average short-changes nobody. The risk is in the averages that are not correctly weighted: a buyer who eyeballs the parcel as "mostly 9ct", or rounds the whole lot down to the lowest carat present, pays you 9ct money for 18ct pieces. If a buyer ever asks to "average" mixed jewellery without separating, treat that as a quiet sign that you should ask for the per-piece breakdown explicitly.

White gold, rose gold and the colour question

A common worry from first-time sellers is that white gold or rose gold is somehow worth less than yellow gold of the same carat. It is not. Carat measures the pure-gold content of the alloy and is unaffected by the colour of the remaining alloy metals. An 18ct white gold ring is 75.0% pure gold and 25% other metals; the "other metals" in white gold are typically palladium, silver and small amounts of nickel (or, in older pieces, plain nickel) which produce the pale tone. An 18ct rose gold ring is also 75.0% pure gold and 25% other metals; the "other metals" in rose gold are weighted heavily towards copper, which gives the warm pink tone. Both are paid for their gold content at the same per-gram rate.

The thing to know about white gold specifically is that almost all white-gold jewellery in the UK is rhodium-plated on top of the white-gold alloy, which gives the brilliant cool-white finish. The rhodium layer wears thin over years of wear, which is why old white-gold rings sometimes look faintly yellowish. The rhodium does not affect the assay or the offer; XRF reads the gold-and-alloy content underneath. If you are looking at a piece that seems "two-tone" because the white plating has worn, that is a sign of age, not a sign of lower carat.