how many state legislatures were required to ratify the 18th amendment
Two-thirds of the states needed to ratify the US Constitution for it to become law. This meant 9 states were needed. However, all 13 of the original states did ratify the Cons â¦ titution with Rhode Island being the last one in 1790.GB.t takes at least 3/4 of the states to ratify an amendment. Since  there are 50 states now, that means you would need at least 38  states for ratification. 2 people found this useful.