Generally, your boots should be the same size as your shoe size. However, the toe shape and heel height may affect how they feel. When purchasing boots, always stand to determine proper fit. There are 3 key "tests" that can be used to determine a proper fit.
The boot shank and arch of the foot should have matching curves. If the smaller toes extend beyond the stitching line of the welt, or if the toes cause a bump, the boots are too short. Examine fit across the instep by taking the leather between your thumb and index finger and rub your thumb across the instep. If the boots are too loose, a large wrinkle will appear.
A slight wrinkle means the boots fit properly.