Buying guide
How to measure a coin for a capsule
Choosing the right capsule starts with one number: the coin's diameter in millimetres. Coins of the same face value can differ between years and mints, so measuring beats guessing. This guide covers how to do it accurately and what to do with the result.
What you need
A pair of digital callipers gives the most reliable reading and costs very little. A steel ruler works at a push, but on a coin only 20 to 40 mm across, a fraction of a millimetre decides whether a direct fit capsule closes properly, so callipers are worth it if you collect seriously.
Measuring diameter
Place the coin flat and measure straight across the widest point, from one edge to the opposite edge through the centre. Take two or three readings at different angles and use the largest. Hold the coin by its edge while you do this; touching the faces transfers oils that speed up tarnishing, which is the very thing a capsule is meant to prevent.
Measuring thickness
Thickness matters for high-relief and proof coins. A standard 1 oz silver coin is around 3 mm thick, but high-relief pieces such as the 2 oz Queen's Beast are noticeably thicker and need a deeper capsule. If your coin is thicker than a normal issue, check the depth figure on the product page, not just the diameter.
Matching to a capsule
Once you have the diameter, match it to the inside diameter shown on each product page, or use the coin size guide, which lists British and world coins by diameter alongside the capsule that fits. Aim for a capsule whose inside diameter is equal to or just above your coin's measurement. If the coin is right at the upper limit of a capsule, a black ring holder removes any chance of movement.
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