You can measure your ring size in several ways and
some methods are more accurate than others.
Of course, the most accurate is if you can get measured by a jeweler,
but if you can't, then you can use one of the methods below.
There is a 0.3mm difference in diameter, and 1mm across the perimeter, between each size, and it is not much, so be careful when measuring your ring size.
The next best thing is if you have a ring that fits the finger you want to find the target on, then you can take a ruler and measure the inside diameter in mm on your ring.
Then you can find your ring size in the chart below.
15.9 mm = size 50 = 50mm
16.2 mm = size 51 = 51mm
16.6 mm = size 52 = 52mm
16.9 mm = size 53 = 53mm
17.2 mm = size 54 = 54mm
17.5 mm = size 55 = 55mm
17.8 mm = size 56 = 56mm
18.1 mm = size 57 = 57mm
18.5 mm = size 58 = 58mm
18.8 mm = size 59 = 59mm
19.1 mm = size 60 = 60mm
19.4 mm = size 61 = 61mm
You can also use this, though more inaccurate method, with a piece of paper.
1: Cut a piece of paper out of approx. 3 x 8 cm.
2: Bend / roll the paper into a roll and insert it into the ring.
Make sure the paper fills the ring completely.
Then cut with scissors in the middle of the overlap.
3: Roll out the paper and measure the distance
between the two marks in mm - this measure is the ring size.
Caution! This measurement method is relatively inaccurate and may have a margin of error of 1-3 sizes.
Use if necessary both methods and compare the result.
If you do not have a ring that fits the desired finger you can
Download this file, with a DIY ring sizer.