A fineness mark gives gold content in parts per thousand: 585 means 58.5% gold. A karat mark gives parts out of 24. Read the entire mark before valuing the piece.
Choose the number actually marked
Use a stamped fineness directly. Nominal 14K is 14/24, or about 58.333%; a 585 input is exactly 58.5%. These are separate calculator choices.
A number is only part of the mark
A UK hallmark has a sponsor’s mark, a millesimal fineness mark and an assay-office mark. A date letter may also appear. A lone number or seller’s description does not establish that an item carries a complete UK hallmark.
Check for a coating
Read letters beside the number. GF, RGP, GP and GEP describe coated construction. Do not enter the whole weight of a gold-filled or plated item as solid gold alloy.