Aught size (11/0)

Aught size is the numbering system used for seed beads, written as a number over a zero like 11/0 or 15/0. The name comes from an old wire gauge term, aught, and the format has stuck for over a century. Sizes commonly run from about 6/0, which is chunky, down to 15/0, which is tiny. The most widely used size for weaving and stringing is 11/0, since it balances visible color with a hole large enough for most needles and thread.

The number matters because it controls two things at once: how big each bead looks in a finished piece and how much thread or wire can pass through its hole. A pattern written for 11/0 beads will come out a different size and density if you substitute 8/0 or 15/0 without adjusting the bead count. Aught size also affects how many passes of thread a hole can comfortably hold in dense weaves.

When buying, check that a listing states the aught size clearly, since vague labels like small or medium are not reliable. Sizes can also drift slightly between brands and even between dye lots, so buy a bit extra when a project depends on consistent sizing. A common mistake is mixing different brands mid-project and then wondering why rows come out uneven, when the real cause is a small size mismatch.