The brush head is 1/4 of an inch.
How large is the brush head?
how long does this brush last i bought it like 5 months ago, and i wash it once a month? when is it time to get a new one?
That's totally up to you! Our brushes are great quality and i've had some for more than 3 years. As long as you clean your brushes, it should last a long time.