THE SHORT ANSWER
Four bullion sizes share one purity but not one transaction cost
The directly documented 2026 bullion range runs from one fine troy ounce to one-tenth ounce, all at 999.9 fineness. Size controls cash per unit, diameter and sale granularity. It does not tell you which coin has the lowest all-in spread.
OFFICIAL 2026 BULLION RANGE
Fine ounces, exact fine grams, diameter and denomination
| Size | Fine gold | Fine grams | Diameter | Face value |
|---|---|---|---|---|
| 1 ounce | 1 troy oz | 31.103477 g derived | 32.69 mm | £100 |
| 1/2 ounce | 0.5 troy oz | 15.551738 g derived | 27.00 mm | £50 |
| 1/4 ounce | 0.25 troy oz | 7.775869 g derived | 22.00 mm | £25 |
| 1/10 ounce | 0.1 troy oz | 3.110348 g derived | 16.50 mm | £10 |
The fine-gram column is a GoldObserve unit conversion, not a second Royal Mint observation. The Mint product records publish fine troy-ounce content and diameter. This table does not invent gross mass where the accessible bullion page omits that field.
WEIGHT LANGUAGE
Fine-gold weight, gross coin weight and fineness are different fields
Multiply stated fine ounces by the same-time price per fine ounce.
Use only a dated official figure for measurement screening.
Do not apply it again to a field already labelled fine gold.
Do not use £100, £50, £25 or £10 as bullion value.
This distinction prevents a common double-discount error: one-quarter ounce is already the pure-metal amount. Multiplying 0.25 by 0.9999 again understates fine content.
SIZE ECONOMICS
Normalize every quote to one fine ounce and one complete round trip
Compare quotes captured close together and under the same delivery and payment assumptions.
Fractional coins can lower the cash needed for one unit and make partial sales easier. The trade-off is often more packaging, handling and fabrication per fine ounce. A one-ounce coin can reduce percentage friction, yet forces the owner to sell a larger unit at once.
The fractional coin wins when smaller future sales and cash control are worth its extra spread. The larger coin wins when a matched dealer ask and bid show a materially lower round-trip loss and unit size will not obstruct the planned exit.
IDENTIFICATION
Diameter narrows the product; it does not prove authenticity
Record year, denomination, diameter, fine content, finish, reverse design, obverse portrait and packaging together. The current four-feature bullion design is not the correct visual reference for every historic, proof or special Britannia.
A measurement conflict is a reason to pause, recalibrate and investigate. A measurement match is supporting evidence only. Continue with the Britannia security guide and proportionate non-destructive testing.
METHOD AND LIMITS
Why the table stops at four bullion products
- Uses individual 2026 Royal Mint bullion product records for the one-ounce, half-ounce, quarter-ounce and tenth-ounce coins.
- Uses the Mint's own labels for pure metal content, diameter, denomination, year, quality and fineness.
- Converts fine ounces with the exact troy-ounce constant and labels the result derived.
- Does not copy proof-only 1/20-ounce and 1/40-ounce sizes into the bullion table.
- Does not assume premium, buyback, availability, gross weight tolerance, mintage or future value.
PRIMARY SOURCES
Royal Mint product records
FAQ
Gold Britannia size questions
What sizes do 2026 Gold Britannia bullion coins come in?
The four directly documented 2026 bullion sizes are one ounce, one-half ounce, one-quarter ounce and one-tenth ounce, all in 999.9 fine gold.
How many grams of gold are in a quarter-ounce Britannia?
One-quarter fine troy ounce equals 7.7758692 grams of fine gold using the exact 31.1034768-gram troy ounce. That is contained fine gold, not a claimed gross coin weight.
Is a £25 Britannia worth £25?
The £25 mark identifies the quarter-ounce denomination and legal-tender status. Bullion value is normally based on contained gold plus or minus the transaction spread, not face value.
Do fractional Britannias always have a higher premium?
Not always, but small units often have higher fabrication and handling cost per fine ounce. Compare actual same-time delivered asks and executable bids rather than relying on a general rule.
Can the size table authenticate a Britannia?
No. Dimensions and fine content help identify and screen an exact product. Authentication also needs provenance, dated design evidence and proportionate professional testing when warranted.