The Danish ring size corresponds to the inner circumference of your finger in millimetres. If you have a finger with a circumference of 54 mm, you use size 54. You can find your size either by measuring the circumference of the finger the ring will sit on, or by measuring the inner diameter of a ring you already wear. You can do both at home with quite ordinary tools.

The quick answer: wrap a thin strip of paper or a piece of string around your finger, mark where the ends meet, measure the length in millimetres with a ruler, and read the number directly as your size. Below, the methods are explained more precisely, along with a table that translates diameter into size if you would rather measure an existing ring.

How to measure your finger's circumference at home

Cut a narrow strip from a piece of paper, or find a thin piece of string. Wrap it around the finger the ring will be worn on, and pass it over the knuckle so it can get past the joint. Place a mark exactly where the strip meets itself, and then lay it flat along a ruler. Read the distance from the start to the mark in millimetres. That number is your ring size.

Feel free to measure two or three times, so you are sure the strip sat snugly without being too tight. If the result falls between two whole numbers, it is usually best to round up to the nearest one, so the ring can get past the knuckle.

How to find the size from a ring you already have

If you have a ring that fits correctly on the finger you are buying for, you can use it as a reference. Measure the inner diameter, that is, the distance across the hole from inner edge to inner edge, in millimetres. Place the ring on a ruler or a piece of graph paper, and read the width as precisely as possible.

The diameter translates into a Danish ring size according to this table:

If your measurement falls between two rows, choose the nearest one. A diameter of 17.0 mm, for example, is closest to 53.

Why the time of day affects the measurement

Fingers change slightly in size over the course of the day. In the morning they are often a little thinner, and after a warm day, exercise or a salty meal they can be swollen. So don't measure right after a run or late on a warm summer evening if you want to hit an average.

Cold contracts the fingers, so a measurement taken with cold hands can give a number that is too small. Wait until your hands are at a normal temperature, and feel free to measure on a couple of different days to see whether the result stays stable.

How tightly should the ring sit?

A ring should be able to go on without difficulty and sit firmly enough not to slide off, but it should still be possible to pull it past the knuckle with a little resistance. When you try on a ring, it is the knuckle that determines whether the size works - the base of the finger itself is usually thinner than the joint.

If the ring sits so loosely that it turns freely or falls off when you shake your hand, it is too big. If, on the other hand, it leaves a deep imprint, or you have to struggle to get it off, it is too small. A well-fitting ring leaves only a light mark that quickly disappears.

If you have large knuckles relative to the base of your finger, you may benefit from choosing the measurement that just barely fits past the knuckle, rather than the one that sits tightest at the base.

The width of the ring matters

A wide ring band covers more of the finger and feels tighter than a narrow one, even when the diameter is the same. If you choose a chunky model, it can be a good idea to go up half a size to a full size compared with a thin ring.

This is worth remembering if you are comparing with a narrow piece of jewellery you already own. A delicate ring such as a round pavé ring or a delicate tiny solitaire bezel ring sits differently from a wide model with stones all the way around. If you need to find the size for a chunkier ring from eternity rings, then allow for the extra width.

Which finger are you measuring for?

The size is individual from finger to finger, and even the right and left hand can vary. The finger you use most often is typically a little thicker. So always measure exactly the finger the ring will sit on - not just any finger on the other hand.

If the ring is to be worn on the ring finger, that is the one you measure. If you are buying for someone else without them knowing, you can borrow a ring that already fits correctly on the desired finger and measure the diameter using the table above.

Pitfalls that give an incorrect measurement

The most common mistake is measuring with a string that is pulled too tight. The finger gives way under pressure, and you end up with a number that is too small. Lay the strip snugly, but without cinching it.

Another pitfall is forgetting the knuckle. If the ring fits perfectly at the base of the finger but can't get past the joint, it will never go on. Always pass the measuring strip over the knuckle before you mark it.

Finally, a wide or stiff piece of cardboard can give inaccurate results because it doesn't lie flat around the finger. Use something thin and flexible so it follows the curve closely.

What to do if you are torn between two sizes

If your measurement falls right between two sizes, the best choice depends on the ring's design. For a narrow ring, you can choose the smaller of the two numbers, so it doesn't slide off. For a wide ring, it is usually wisest to go up, because the band takes up more space.

If you measure several times and get different results, use the average rather than the single extreme. A few extra measurements at different times give a more reliable picture than a single reading.