Average Amount of Botox Units to Lift Brows?

Botox only works about half of the time to raise lateral eyebrows. It looks great when it does work but don't be disappointed if it doesn't do it every time. 

Thank you for your question. Shaping the brows is one my favorite parts of using Botox. It requires a very detailed understanding of the underlying anatomy as well as assessing each individual while they are animating their brows. By carefully placing Botox in the muscles that depress the brow, you can cause the brow to rest and relax in a lifted position. There are limits to how much you can lift, and for some surgery is better option. Incorrect assessment or placement can also lead to the reverse effect, so overall technique is critical. You can also shape the brow different. For example, you can raise the tail of the brow vs creating a raised arched brow vs creating a raised horizontal brow. It depends on the individual's desired brow aesthetic goals. I would consider this a very advanced technique so I would query your injector on their experience in this area.
As far as how many units may be needed, this also depends on which part of the brow you want to correct. For the inner brows, you may consider ~20 units (same as the frown line treatment). For the middle or outer brow, I generally use up to 5 units on each side.
You may also want to consider adding fillers to shape and raise the brow. Combining the two products can work synergistically together.

Generally I use 2 1/2 -4 units each side to lift the tail of the brow. It is injected more superficially than other areas and should be done by an expert injector. Botox is a muscle paralyzing substance that is injected into or near facial muscles by a doctor or nurse injector to weaken or prevent it from working for a period of months.It may seem counter-intuitive that paralyzing facial muscles can lift your brow, but this is exactly how Botox works. Our faces have muscles that pull in opposing directions, so in the case of the brow the idea is to paralyze the muscles that pull downward while leaving the ones that lift the brow untouched.

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.