This is a free tool to help you find your US ring size. How to measure your finger using the Ring Sizing Tool. Wrap the reusable gauge around your finger. Threading the end through the channel. It should fit your finger comfortably; snug enough so that it will not fall off, but loose enough to slide over your knuckle. Note the number that the black arrow points to. Notches between the two correspond with half sizes. When to measure you finger Finger size changes depending on the time of day and the weather. For best results measure your finger size: At the end of the day and when your fingers are warm (fingers are smaller in the early morning and when cold. Measure finger size 3 to 4 times to eliminate an erroneous reading. Be aware that the sizes on the two hands can vary a lot. So make sure to measure the actual finger where you would wear the ring. Please be aware that ring sizes shown on the website reflect ring sizes by each designers country. If you already know your size, using another countries measure, you can use the International Ring Size Chart to convert your size to the corresponding size from your country.