Gold is graded according to its purity. Pure gold is 24-karat and is normally found in coins like full sovereigns, half sovereigns or in gold rings. The spot price is based on 24K gold.Most gold jewelry has had metals mixed in with the gold to strengthen the piece. So jewelry is worth less than pure gold depending on its karat rating.
Most jewelry will have a karat number on it.

Gold buyers sometimes run acid or electronic tests, which will confirm the purity of the gold.
The lower the karat rating, the lower the amount of gold in an item.

* 18-karat gold is 75% gold
* 14-karat gold is 58.3% gold
* 12-karat gold is 50% gold
* 10-karat gold is 41.7% gold

When selling gold jewelry, always check to see if it is 9k, 14k, 18k or 24k Gold.

Some gold buyers use scales which are set to grams. There are 31.1 grams in a troy ounce.
Once you know the type of gold you own and its weight, you have a starting point to negotiate a price.