To determine the cost of a 12g gold ring, we need to consider several factors, including the purity of the gold (which is often measured in karats), the current market price of gold, and any additional costs such as craftsmanship, design, and brand.

Gold purity is often expressed in terms of fineness or karat (kt)、Common purities include:

24K (99.9% gold): This is considered pure gold but often alloys are added for strength.
22K (91.6% gold): Common in jewelry, offering a good balance between purity and durability.
18K (75% gold): Popular for its bright color and durability.
14K (58.3% gold): More durable and less expensive, often used for intricate designs.

The price of gold fluctuates daily、As of my last update, the price of gold per gram can vary, but let's use a hypothetical price for calculation purposes、Assume the current market price for 24K gold is about $60 per gram (this can vary significantly based on market conditions and the specific alloy).

For 24K Gold:
12g of 24K gold at $60 per gram would be $720.

For 22K Gold:
If 22K gold costs slightly less per gram due to its lower purity, let's assume $55 per gram.
12g of 22K gold would be $660.

For 18K Gold:
If 18K gold is priced at $45 per gram (a rough estimate),
12g of 18K gold would be $540.

For 14K Gold:
If 14K gold is priced at $35 per gram,
12g of 14K gold would be $420.

Keep in mind, these are rough estimates and do not include:
Making charges: These can vary widely depending on the complexity of the design and the craftsmanship involved、This can add anywhere from 10% to 300% or more to the cost of the gold itself.
Retail markup: Jewelry stores often have significant markups.
Diamond or gemstones: If the ring includes any stones, their cost can greatly increase the price.

To give you a more accurate estimate, I would recommend checking with local jewelers or online retailers for current prices and offers、Additionally, the prices mentioned above are purely for the gold content and do not reflect the final retail price of a gold ring, which can be significantly higher due to design, craftsmanship, and brand value.