To measure for a ring:
This handy chart gives a conversion for worldwide ring sizes, so that you convert the UK sizes shown to your own countries sizing. You can also measure the inside diameter of a ring you currently own. Find a ring that fits the finger you would like to wear your new ring on by placing the ring onto a ruler or tape measure. Take the measurement from side to side of the centre of the inside of the ring to find the diameter (this is much easier than trying to find the inside circumference!) This measurement will convert to your ring size in letters, giving you the size you need to order.
You can also measure your finger with a tape measure or piece of string- make sure that the measurement is close fitting to your finger, but that it will fit over your knuckle. mark where the measure/string overlap, and find the size against a ruler if using string.
It’s best to measure your ring size when your hands are warm/hot- so that your ring fits when your fingers swell a little from heat.