Ideally you should use the appropriate ring gauge to determine your ring size, which any jewellery retailer should have. It is possible to achieve an approximate size by measuring the circumference of your finger using a stiff piece of material or pliable plastic if it is done carefully. Tape this material together into a ring shape and mark the inside join, open the ‘ring’ and measure in millimetres. Translate this to the appropriate system on our finger size chart.

Remember to allow for the size of your knuckle; a well fitting ring will catch slightly on the knuckle but should not feel too tight when you clench your fist. Also a wide band ring will catch more on the knuckle and cling more to the finger, which usually necessitates a larger size, perhaps as much as one or two sizes.

It is generally easier to put a ring on than to take it off. When measuring finger size, your hands should be warm but not hot because fingers swell in the heat.

Do not push on a ring with excessive force as it is usually easier to put it on than to take it off. 
 

If you are purchasing on behalf of someone else and you have legitimate access to a ring which they wear, you could take it to a jewellery shop and have it measured. But check if it is for the same finger, same hand, or whether it still fits. The measurement of a ring should be read from the leading edge i.e. the edge which reads the largest. 
Do not push on a ring with excessive force as it is usually easier to put it on than to take it off.


Comparing UK sizes to other systems

The UK system is known as Wheatsheaf, developed in 1945 based on diameter divisions of 1/64 inch. The system underwent metric conversion in 1987 when each full size equalled 1.25mm of circumference, taking a baseline of size C = circumference of 40mm.

The USA and Japanese sizes are listed according to their nearest equivalents and are accurate enough for all practical purposes. One full USA size is equal to 2.6mm of circumference. Japanese sizes relate to diameter; size 1 being 13mm, each full size would add one third of a millimetre.

European sizes are the circumference minus 40 mm, therefore when translating your size to UK simply look for your nearest whole or half number e.g. 50mm circumference minus 40mm equals size 10 or UK size K.

Incidentally Japanese size 10 is the same; smaller sizes are almost the same as European but change more as they increase in size.

Please note the figures for circumference and diameter are in millimetres and are internal measurements. These are the measurements which equate with the ring size. You can not calculate a ring size by its external circumference unless you factor in the thickness of the ring.