From what I have researched, 400mg for women who are not pregnant, 800mg for pregnant and lactating women. However, if the woman has given birth to a child w/ a neural tube defect, Dr's recommend that more folic acid should be taken in order to prevent another neural tube defect.
Also, Folic acid is water soluble. So you can't take "too much". Your body will release the vitamin if you take too much. You can't overdose or have adverse effects from taking more than you need.
Hope that helped!