Seed beads and needles use a similar gauge (the smaller the number, the larger the bead or needle).

If you're working with seed beads, or if you have a sense of their hole sizes and can mentally compare them to the beads and stringing material you plan to work with, a good rule of thumb to follow in selecting a needle is to buy at least one size smaller than the seed bead size. For example, if you're working with beads with holes that are equivalent to 11/0 seed beads, then use a #12 needle.