Working just like a belt, slip the Multisizer ™ ring sizer onto your finger, adjust for a comfortable fit and read off the size indicated by the arrow. Available in AUS sizing. This Multisizer ™ can be used over and over, it's not a disposable product.
 
Note: Make sure you can get it over your knuckle and perhaps try over few different times in the day, as hands swell during the day/night and in warmer climates.