4. SizeScale. Your vanity size should always make sense for your bathroom's size. Cramming a huge vanity into a tiny bathroom doesn't make sense, no matter what your storage needs are. "The amount of storage required by the client impacts the size of the vanity," says Lawson. "But more important is the size of the room it sits in. Working within the architecture is part of the equation." "By evaluating lifestyle, whether a powder room or master bath, and the demands that will be placed on the vanity, the size will become evident quickly," says O'Neill. For regularly used bathrooms, Adamson recommends starting with a vanity that's a minimum of 21 inches deep and 24 inches wide.