Everyone's hands are slightly different, so you might want to practice and calibrate your own hand measurements using the Big Dipper.

Here are the rough distances from Dubhe to several other prominent Big Dipper stars:

Dubhe to Merak	5 degrees
Dubhe to Megrez	10 degrees
Dubhe to Alioth	15 degrees
Dubhe to Mizar	20 degrees
Dubhe to Alkaid	25 degrees