Hair on average grows half an inch per month. So for it to grow three inches, it'll take up to six months.
But don't worry, you can fasten your hair growth with vitamin E supplements, cod liver oil. And when it grows an inch or two:
"Choose products that contain ingredients that are healthy for hair. Ingredients like avocado, coconut, jojoba, and olive are all beneficial when used in moderation. They help retain moisture and oils while minimizing split ends and other hair damage."