Method 3 - Measure your finger
Use a measuring tape and wrap it around your finger.
If you don't have a measuring tape, you can use a piece of paper and ruler. Wrap the piece of paper snugly around your finger, mark the spot where the paper ends meet. Place the paper on a table and measure it with a ruler.
Size 5: 49.3 mm
Size 5.5: 50.6 mm
Size 6: 51.8 mm
Size 6.5: 53.1 mm
Size 7: 54.4 mm
Size 7.5: 55.7 mm
Size 8: 56.9 mm
Size 8.5: 58.2 mm
Size 9: 59.5 mm