It can be difficult to know the size on your fingers if you have never had a ring before. If you have a ring sinze before, you can measure the inner diameter of the ring with a slider to find the size you need. If you have no ring to measure, take a string, wrap it around the finger you want the ring on and measure the length of the string. Then you get the circumference. To convert it to diameter, divide it with pi (3.14) Some things to keep in mind when measuring your size are that sizes can vary between different models. A thin ring usually feels larger thaan a wide ring. Also consider whether you are hot or cold. In the summer, if it is hot, your fingers will normally swell a bit, if it is cold your fingers will become narrower.