If you’ve seen 18K, 18ct or 750 stamped on gold jewellery, you may wonder what these marks mean.
In simple terms, 18K gold contains 75% pure gold. Understanding carat, fineness and hallmarking can help you make a more informed purchase, particularly when buying gold jewellery online.
At T.ELLE, we specialise exclusively in 18K gold jewellery, so we believe our customers should understand what 18K means, how it relates to 750 gold and why a UK hallmark matters.
What Does 18K or 750 Gold Mean?
18K, also written as 18ct, means that jewellery contains 18 parts pure gold out of 24:
18 ÷ 24 = 75% pure gold
The remaining 25% consists of other metals, which are added because pure gold is relatively soft. These metals help improve the strength and durability needed for everyday jewellery such as rings, necklaces, bracelets, earrings and pendants.
You may also see 750 used instead of 18K or 18ct. They describe the same gold purity and fineness:
750 parts gold ÷ 1,000 = 75% gold
Therefore:
18K gold = 18ct gold = 750 gold = 75% gold
The UK hallmarking system recognises 750 as the fineness standard for 18-carat gold, which is why you may see 750 as part of an 18K gold hallmark.
What Is a UK Gold Hallmark?
A UK gold hallmark is an independent mark applied after precious metal jewellery has been tested. It verifies that the item meets its stated gold purity standard and provides important consumer protection, since gold purity cannot be determined by appearance alone.
For qualifying gold jewellery sold in the UK, hallmarking is legally required. The compulsory hallmarking threshold for gold is 1 gram.
This is particularly useful when buying gold jewellery online, where you cannot physically inspect the piece before purchasing.
A full UK hallmark contains three compulsory marks:
1. Sponsor's or Maker's Mark
This identifies the company or person responsible for submitting the jewellery for hallmarking.
2. Fineness Mark
This shows the precious metal content.
For 18K gold, the fineness mark is:
750
This means the alloy contains at least 750 parts gold per 1,000.
3. Assay Office Mark
This identifies the UK Assay Office where the jewellery was tested and hallmarked.
The four UK Assay Offices are:
London • Birmingham • Sheffield • Edinburgh
A date letter may also appear, but this is optional.
Why Does Hallmarking Matter When Buying Online?
Hallmarking provides reassurance that the stated precious metal content has been independently verified.
When buying gold jewellery online, it is worth looking beyond photographs and asking:
- Is the jewellery 18K, 18ct or 750 gold?
- What is its weight?
- Is it hallmarked, and where was it tested?
- Does the seller provide clear fineness and authenticity information?
These simple questions can help you understand exactly what you are purchasing and compare gold jewellery with greater confidence.
18K Gold Compared with Other Purities
Gold| Fineness| Approx. Gold Content
9K / 9ct| 375| 37.5%
14K / 14ct| 585| 58.5%
18K / 18ct| 750| 75%
22K / 22ct| 916| 91.6%
Different gold purities have different levels of gold content. This can affect the composition, colour, durability and price of jewellery.
Understanding carat and fineness makes it easier to compare different gold options and choose what is right for you.
Why T.ELLE Chooses 18K Gold
At T.ELLE, we specialise exclusively in 18K gold jewellery.
Our 18K gold jewellery is independently tested and hallmarked in the UK, with a Certificate of Authenticity provided with our jewellery.
We want our customers to feel confident about the gold they are purchasing — not simply its appearance.
For us, quality is about transparency as well as design.
What Should You Check Before Buying Gold Jewellery?
Before purchasing gold jewellery, especially when buying online, consider checking:
✔ Gold purity
Look for a clear indication such as 18K, 18ct or 750.
✔ Weight
Gold weight helps you understand and compare different pieces.
✔ Hallmarking
For qualifying items, look for a recognised UK hallmark.
✔ Authenticity and seller information
A reputable seller should clearly explain the gold used and provide relevant authenticity information.
✔ Delivery and insurance
For higher-value jewellery, check how your order will be delivered and whether it is insured.
The Bottom Line
18K, 18ct and 750 refer to the same basic gold purity standard: 75% gold.
When buying gold jewellery in the UK, a hallmark provides important information about its fineness and where it was independently tested.
At T.ELLE, we believe buying gold should feel as good as wearing it — with transparency, authenticity and confidence at every step.
18K Gold. UK Hallmarked. Certificate of Authenticity.
T.ELLE — Rooted In Royalty.