Wrap the strip of paper tightly around your desired finger.
Using a pen or pencil, mark the point where the paper overlaps itself.
Lay the strip of paper on a flat surface and use a ruler to measure the distance from the end of the strip to the marking you made, in millimetres. This will give you a measurement of the circumference of your finger.
Using the below chart, convert your measurement into a standard US ring size.
If you are in between two sizes, it is always best to round up rather than down.