What 18ct gold means and why it is the classic wedding ring gold

What is 18ct gold?

18ct gold is an alloy that is 75% gold by weight. Carats count gold in 24ths, so 18 carat means 18 parts in every 24 are pure gold and the other 6 parts are other metals. In parts per thousand that is 750, which is the number stamped inside an 18ct ring.

The other quarter does two jobs. It gives the gold its colour (yellow, white or rose) and it makes the metal hard enough to wear. Pure gold is too soft for a ring worn every day, so every gold wedding ring is an alloy. 18ct simply keeps more of the gold than 9ct or 14ct does.

That is where its reputation comes from. With three quarters of the ring being gold, 18ct has the warmest, deepest yellow of the gold alloys and the most weight in the hand. It is the metal most people picture when they picture a wedding ring.

What is 9ct gold?: The other British gold standard: 37.5% gold, hallmarked 375, harder and lighter than 18ct.

What does 750 mean on a ring?

750 is the fineness mark for 18ct gold. It means an assay office tested the ring and found at least 750 parts of gold in every thousand before striking the mark. The figure is a minimum, never an average.

In Britain anything sold as gold that weighs more than one gram has to be hallmarked. Every wedding ring is well over that weight. A full hallmark has three compulsory parts: the sponsor's mark, showing who sent the ring for testing; the fineness mark, 750 for 18ct; and the mark of the assay office that tested it. A date letter is optional.

So a 750 inside the band is your proof the ring is 18ct. The hallmark decoder reads the rest of the mark, including which assay office struck it.

Hallmark decoder: Enter the numbers and symbols inside a ring and see the metal, its fineness and the assay office that marked it.

UK hallmarks explained: What each mark tells you and which rings have to carry a hallmark by law.

Is 18ct gold good for a wedding ring?

Yes. It is the traditional choice for good reasons: the richest colour of the gold alloys, real weight on the finger and a metal that can be polished, resized and passed down.

It is the heavier gold. A plain court band in UK size N weighs about 2.5g at 2mm, 5.1g at 4mm, 7.6g at 6mm and 10.2g at 8mm in 18ct yellow gold, from the density in our ring weight model (15.7 grams per cubic centimetre). The same 6mm band is about 5.5g in 9ct and 9.8g in platinum 950. If you like to feel your ring, 18ct gives you that.

It is a little softer than 9ct, about 3 on the Mohs scale against 3.5, so it shows everyday marks a little sooner. On gold those marks soften into a gentle satin and polish back to a mirror shine at any jeweller. If you work with your hands and want gold that keeps its finish longer, 9ct is the harder wearing of the two.

18ct gold or 9ct gold?: The two side by side: weight at every width, hardness, prices in our range and resizing.

Ring weight calculator: Set your own size, width and thickness and see what the band weighs in each metal.

What colours does 18ct gold come in?

Yellow, white and rose. Our 18ct rings come in all three. Each is 75% gold. The colour comes from the other 25%.

White gold is gold alloyed with white metals. GIA lists nickel, palladium and zinc; the reference 18ct white casting alloy in our weight model is whitened with palladium and is denser than yellow, at 16.4 against 15.7 grams per cubic centimetre, so a 6mm band in size N comes to about 8.0g. White gold is usually rhodium plated for a brighter white and a better shine. The plating wears gradually and a jeweller replates it whenever the ring starts to look warm.

Rose gold is gold alloyed with copper and silver, which gives it its pink warmth. GIA advises anyone allergic to copper or nickel to look at platinum instead; our guide to metal allergies covers the metals that suit sensitive skin.

Metal allergies and hypoallergenic rings: Which ring metals suit sensitive skin and what to look for in white gold.

Can 18ct gold be resized? How do you look after it?

Yes, it can be resized. A plain 18ct gold band can be made larger or smaller by a jeweller, the way wedding rings have always been resized. The exception is a band set with stones all the way round, where there is nowhere to cut without disturbing a stone, so on those the size is settled when you order.

Looking after it is simple. Mild soapy water, a soft brush and a soft cloth bring back the shine at home. Take it off before a chlorinated pool or household cleaning, because chlorine bleach can damage gold alloys. A jeweller's polish takes a very small amount of metal each time, so it is an occasional refresh rather than a routine.

Every ring we make is made to order in your size. The free ring size finder measures your finger at home in a couple of minutes.

Gold rings: Every gold band in our range, in 9ct and 18ct, made to order in your size.

How to look after a wedding ring: Cleaning and care for gold, platinum, titanium, zirconium and diamond rings.

Ring size finder: Measure your ring size at home in a couple of minutes.