How Much Gold Is in the Bar? Read the Weight and the Assay Together

Read the noun after the number

A gram measures mass. Fineness describes the share of that mass that is gold, conventionally expressed in parts per thousand. A fine troy ounce expresses the mass of gold after accounting for that share. A number printed beside “gross” therefore plays a different role from one printed beside “fine gold content.” Even a meticulously calibrated scale cannot resolve an ambiguous label.

On an invoice I would transcribe the wording before making a spreadsheet. Does the listed weight include a frame, clasp, capsule or decorative setting? Is the certificate tied by serial number to the item in hand? If the documents specify a quantity of fine gold already, use that quantity directly. Applying the purity fraction again counts the alloy twice.

Source notes: [1] LBMA — Good Delivery Rules, Annex C, Weight Lists

Convert one sample lot by hand

Consider a hypothetical unpackaged 100.000 g bar with stated fineness 999.9 parts per thousand. Divide 999.9 by 1,000 to get 0.9999. Multiplying the gross weight by that fraction gives 99.990 g of fine gold. Divide by 31.1034768 g per troy ounce and the result is approximately 3.21475 fine troy ounces. Keep the unrounded figure in the worksheet until the final display.

For comparison, a hypothetical 100 g piece of 750-fine alloy contains 75 g of gold, approximately 2.41131 fine troy ounces. The same gross weight now describes a materially different exposure. If someone quotes gold per fine ounce, use the fine-ounce column. A dealer’s whole-item quote can also reflect craftsmanship, condition and resale demand. The metal-content calculation alone cannot reproduce it.

Source notes: [1] LBMA — Good Delivery Rules, Annex C, Weight Lists · [2] LBMA — Purity of Gold

Check what the certificate can establish

An assay is a measurement of composition. LBMA’s testing guidance explains why a representative sample matters when determining the fineness of an entire bar. A surface measurement and a matching gross weight can provide information while leaving the interior composition uncertain. I would describe an unverified hallmark as a stated fineness and retain the certificate or assay details separately.

Formal London bar weight lists also have prescribed conversion and rounding conventions. The worked retail-sized examples here use simple mass arithmetic. If a published wholesale fine weight differs slightly from an unrounded calculator result, read the applicable weight-list procedure before claiming the documents disagree.

Source notes: [1] LBMA — Good Delivery Rules, Annex C, Weight Lists · [3] LBMA — Physical Market Guidelines

Make the estimate reproducible

My record for the sample has five entries: gross metal mass, original unit, stated or independently measured fineness, fine mass and evidence identifier. The price, currency and time of any subsequent valuation belong on a separate line. If the metal mass excludes a stone but the original receipt includes it, I keep both figures and their labels. Someone else can then recalculate the estimate without guessing which object was on the scale.