Rings and gauges are hard metal objects that can be measured exactly, but your finger is flesh and bone. Your finger is not round and it cannot be measured with the same degree of accuracy as the ring. At the end of the day, the right ring is one that will stay on comfortably. Average ring finger sizes may be useful as a point of reference for people who are not very good at measurements. These are offered to help you know if your calculations are reasonable.
Average adult women size 6 to 8 or L to Q
Most American jewelers
get women's samples in size 7
Average adult man size 9 to 11 or J to W
Most American jewelers
get men's samples in size 10
Finger sizes sometimes do not correspond to body size. Finger sizes also are prone to change with temperature, humidity, exercise, what you have been eating, time of day, time of the month, pregnancy and other factors. Dominant hand is usually 1/2 size larger, so if you are right handed and have a size 7 ring that fits the left hand it is reasonable to guess that a 7 1/2 will fit the right hand. Quarter sizes are offered to help you get the best fit, however quarter sizes make more difference on smaller fingers than on large fingers.
The best size is usually the ring that fits snugly and gives a little resistance when you take it off. Wider rings should be a little looser that narrow rings.
Men take note that if you are not used to wearing a ring, the proper size will probably feel tight a first. Many men loose their wedding rings because they choose sizes that are too loose. | 
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