Don’t measure when your body temperature is either too cold or too hot. A cold finger shrinks while a hot finger expands causing an inaccurate reading. Exercise, salt, alcohol, hormones, etc. all make your fingers swell. Lack of sleep and flying on planes generally makes hands swell.
When two sizes seem to fit
If you are between two sizes, go with the larger one.
Don’t use strings
Strings tend to stretch, which can result in a wrong size.
Big knuckles can affect your size
If your knuckle is larger than the base of your finger, you may need to go up a half size.
A wider band needs a bigger size
If you are purchasing a wide band, you will be more comfortable moving up a half size from your measurement.