Use a troy ounce
The ounce used for precious-metal pricing is the troy ounce, equal to 31.1034768 grams. It differs from the ordinary ounce used for other weights. A factor of approximately 28.35 grams is therefore not the correct conversion for a quoted troy ounce of gold.
Convert weight, then price
Multiply troy ounces by 31.1034768 to obtain grams. Half a troy ounce is 15.5517384 grams. To convert grams into troy ounces, divide by the same factor. A kilogram is 1,000 grams.
For a price quoted per troy ounce, divide by 31.1034768 to obtain the nominal price per gram of fine gold. A karat adjustment can then multiply that gram price by K/24. Check that both the quote and the weight refer to the same metal.
Check what the weight includes
Keep the full conversion factor during calculation and round only the displayed result. Rounding every intermediate step can compound differences across large weights or several items.
A coin or bar description may state both total product weight and fine-metal content. Jewellery may include stones or non-gold components. Do not enter gross weight as pure gold, and do not apply a purity adjustment twice when a stated weight already represents fine gold. Record the unit alongside every amount so a later comparison remains clear.