First of all, we should note that we do not typically say that the Declaration of Independence was “ratified.” We typically reserve that term for the Constitution. The Declaration of Independence did not set up any specific system of government. It was not a constitution. Therefore, we do not typically refer to its ratification.
At the time that the colonies declared independence, there was no set constitution. The Articles of Confederation would not be ratified for years after 1776. Therefore, there were no rules about how many states would have to vote on a declaration of independence.
As it turned out, 12 of the 13 colonies did vote in favor of independence on July 1, 1776. New York did not vote because its delegates felt that they needed to get explicit instructions from their constituents. After the delegates got those instructions, they voted in favor of independence on July 9.
While there was no set number of states/colonies that had to vote in favor of the Declaration, the members of Congress felt that it was important that such an important vote be unanimous. Therefore, they waited until all of the colonies were in favor.
Thus, there was no official rule about how many states had to ratify it. Unofficially, Congress wanted to have a unanimous vote.