Average Amount of Botox Units to Lift Brows?

A very general dosing would be 20 units to the glabellar area to lift the inner brows while relaxing the muscles reponsible for the "11's" or frown lines.  In addition, dosing the lateral  or outside tail end of the eyebrows at a key point with 5 units each side is a nice way to compliment the brow lift.  Some will benefit from dosing along the eye muscle as well.

Make certain that you choose a practitioner that understands your goals and tailors the treatment plan to meet those goals.

The below link offers further information on brow lifts with Botox.

29 units to 39 units is a reasonable range. This would be enough to treat the area between the eyebrows which normally pulls down on the middle forehead, and the tail of the eyebrow. These areas pull down in opposite vectors from the forehead muscle that wants to pull up. When their motion is inhibited by the Botox, the antagonistic forehead muscle can pull up simulating a lift (although surgery would provide a better result).

If you get your frown muscles injected along with the depressor muscles of the tail of your eyebrows (corrugator muscle and orbicularis muscles), you should see elevation of your eyebrows. This could be achieved with between 25 and 37.5u of BOTOX Cosmetic.
I hope this is helpful for you.