1. Cut yourself a strip of paper roughly 10mm thick
2. Wrap the strip of paper tight around the base of your finger
3. Make a mark where the strip of paper intersects.
4. Grab a ruler and measure in between the marks.
5. Use this size chart to convert the your measurement (in mm) into your size (we  work in Aus sizing)
6. Order yourself that size and Bob’s your uncle. 

You can also measure the diameter of an old ring to get your size.