The fastest way to your answer: measure the inner diameter of a ring you already wear, in millimetres, and look the number up in the table further down. An inner diameter of 17.2 mm corresponds to size 54, and 15.9 mm corresponds to size 50. The ring size in Denmark is namely defined by the circumference of the finger in millimetres, and it can be derived directly from the diameter of a ring that fits.

If you don't have a ring to measure, you can instead measure the finger itself with a piece of string or a strip of paper. Both methods work from home, and they typically hit within one size of the correct one when carried out carefully.

Below we go through the three most reliable ways to find the size, what time of day you should measure, and how to read the table correctly.

How to measure the diameter of a ring you already wear

Take a ring that fits well on the finger you're going to use the new ring for. Lay it flat, and measure the distance across the inside from edge to edge. That is the inner diameter, and it should be measured in millimetres with a ruler where you can read half millimetres.

Precision matters a lot here. A difference of less than a millimetre moves you a whole size, so measure two or three times and use the average. If you measure 16.6 mm, you land on size 52; if you measure 16.9 mm, you're up at 53.

This method is the most reliable, because it is based on a ring that demonstrably fits. Be aware that a wide ring band often requires a slightly larger size than a narrow one, because it covers more of the finger.

How to measure the finger with string or paper

If you have no ring to go by, you can measure the finger's circumference. Wrap a piece of string or a narrow strip of paper around the finger where the ring is to sit, and mark with a pen where the end meets the rest. Then lay the string flat and measure the length from start to mark in millimetres.

That length is the ring size itself. If the circumference measures 54 mm, you use size 54. The system is simple, because the Danish ring size and the finger's circumference in millimetres are the same number.

The string should sit snugly, but not tight. If you pull too hard, you'll get too small a result, and the ring can be difficult to get on. If, on the other hand, the measurement sits loosely, you risk a ring that slides off too easily.

What time of day should you measure?

The size of the fingers changes throughout the day. They are smallest in the morning and after cold, and they are largest late in the day, in heat and after physical activity. Therefore measure in the middle of the day at normal body temperature, when the finger is closest to its average.

Avoid measuring right after exercise, a hot shower or a meal with a lot of salt, when the fingers can be swollen. If you're in doubt between two sizes, the slightly larger one is often the most comfortable choice for daily use.

Diameter and circumference converted to Danish ring size

The table here ties the two methods together. If you've measured the diameter of a ring, you find the size in the left column toward the middle; if you've measured the finger's circumference with string, you read directly in the size column, since circumference and size are the same number.

If your measurement lies between two rows, round up to the nearest. A diameter of 17.0 mm places itself between 53 and 54, and here size 54 is usually the most comfortable.

How tightly should a ring sit?

A ring should be able to be pushed on without difficulty and sit firmly enough that it doesn't fall off, but it should still be able to be pulled over the knuckle with a little resistance. The knuckle is often wider than the finger itself, and it is what determines whether the ring can get on and off at all.

If the ring sits so loosely that it turns freely around all the time or slides toward the fingertip when you lower your hand, it is too big. If, on the other hand, you can't get it over the knuckle without using soap or force, it is too small. The goal is a ring that meets slight resistance at the knuckle and then rests calmly at the base of the finger.

The width of the ring affects the size

The wider the ring band, the more of the finger the ring covers, and the tighter it feels at the same size. A wide model like a medium eternity ring with diamonds all the way around sits closer than a thin, smooth ring in the same size.

If you choose a strikingly wide ring, it can therefore be worth going half to a full size up compared to what you normally wear. A narrow tiny solitaire bezel ring can conversely be worn in your usual size without adjustment. If you're considering a heavier model, it can help to see the overall statement rings and eternity rings with wider bands.

Are you measuring for another person?

If the ring is to be a surprise, the most discreet method is to borrow a ring the person already wears on the correct hand, and measure the diameter using the procedure above. Make sure that the borrowed ring belongs to the finger the new ring is to sit on, because fingers are rarely identical.

The right and left hand often have different measurements on the same finger, and the dominant hand is typically slightly larger. If you don't know the finger precisely, a ring with a simple, classic fit is a safe choice, because it is easier to adjust afterwards than a model with stones all the way around.

What if the ring doesn't fit after all?

A ring with a smooth band or a single centre stone can in many cases be adjusted up or down in size at a jeweller's. It is harder with rings where the diamonds run all the way around the band, as with an eternity ring, because the setting itself is fitted to a particular circumference.

That's why it's an advantage to hit the size as precisely as possible from the start, especially if you're looking at a model from rings where the stones sit close together. If you're in doubt between two sizes on a ring that can't easily be changed, it carries a lot of weight to measure carefully at several times before you decide.