If you have taken gold to a buyer in the United States, the offer was probably quoted per pennyweight rather than per gram. That unit choice is worth understanding, because it makes the same offer look considerably larger than it is.
A pennyweight is 1.55517 grams. It is one twentieth of a troy ounce, which is itself 31.1035 grams rather than the 28.3495 grams of the ordinary avoirdupois ounce used for groceries. So a price quoted per pennyweight is roughly 1.56 times the equivalent per-gram price for the same metal. Nothing dishonest is happening, but if you are comparing one buyer quoting per gram against another quoting per pennyweight, you are not comparing like with like until you convert.
The second thing to get straight is what karat actually measures. Karat is fineness out of 24, so the purity ratios are fixed regardless of what the market is doing:
- 24K is 0.999 fine, effectively pure
- 22K is 0.9167
- 18K is 0.75, exactly three quarters gold
- 14K is 0.585, the 585 European hallmark standard
- 10K is 0.4167, the lowest that may be sold as gold in the US
Those ratios are the stable part of this. A 14K item contains 58.5 percent gold by weight whatever the spot price is, so its melt value is 58.5 percent of the pure-gold value of the same weight. That is the whole calculation: weight, times purity, times the current spot price per unit of weight. Any figure a buyer quotes that is well below that is the buyer's margin, not a different valuation of the metal.
Two practical consequences follow. First, always convert both offers to the same unit before deciding, and be explicit about whether a quoted "ounce" is troy or not. Second, weigh mixed-karat items separately. Averaging a 10K chain with an 18K ring gives a number that does not correspond to either piece, and since the purity ratio between them is nearly 1.8 to 1, that averaging can be expensive.
Deliberately no dollar figures here. Gold moves daily, and a stale per-gram number is worse than none, so the reference table behind this post is used only for the purity and unit relationships, which do not move.
A live per-gram and per-pennyweight calculator by karat is at goldgramprice.com.