Seed Bead Size Chart
Seed bead sizes run on an inverted aught (/0) scale where the number gets smaller as the bead gets bigger, which trips up nearly every beader at least once. This chart lists the diameter, approximate beads per inch, and typical use for every common size from the largest (3/0) to the smallest widely available (18/0), plus notes on cylinder beads, needle sizing, and manufacturer variation, so you can convert between a pattern's stated size and what is actually in your hand.
How the aught (/0) sizing system works
The aught system, written as a number followed by a zero or a degree symbol (11/0, 11°), originated with the drawn-glass rod diameters used decades ago and has stuck despite being backwards from how most sizing systems work. A higher aught number means a smaller bead: 15/0 is tiny, 3/0 is chunky. There is no fixed formula converting aught to millimeters, since the standard predates precise machine manufacturing, so every size below is an approximate range you will see confirmed (with small variation) across Miyuki, Toho, Preciosa, and other major seed bead brands.
Two beads of the same stated aught size from different manufacturers are rarely identical. Toho and Miyuki round beads run close to each other in most sizes, but Czech seed beads (Preciosa) tend to run slightly smaller and more irregular in shape than their Japanese counterparts at the same nominal aught, which matters when a pattern calls for a precise fit, such as peyote or brick stitch where uniform bead height carries the row.
Size chart: 3/0 down to 18/0
3/0 (3°): approximately 5.5 to 6mm diameter, roughly 4 beads per inch strung. The largest size in common use, mostly seen as spacers, in bold statement jewelry, and in some loom and bead crochet work where scale matters more than fine detail.
5/0: approximately 4.5mm diameter, about 5 to 6 beads per inch. Used for chunkier stringing projects and as a transitional accent size between pony beads and standard seed beads.
6/0 (also called E-beads): approximately 4mm diameter, around 6 to 7 beads per inch. A popular size for fringe, embellishment on larger pieces, and as a stopper bead, and one of the easiest sizes for beginners and children to handle because it is large enough to see and grip easily.
8/0: approximately 3mm diameter, roughly 12 to 13 beads per inch. A workhorse size for bead weaving, especially right-angle weave and herringbone, and for stringing projects that want visible individual beads rather than a fine, dense texture.
10/0: approximately 2.3 to 2.5mm diameter, about 15 to 16 beads per inch. Less commonly stocked than 8/0 or 11/0 but sits usefully between them for patterns that want finer detail than 8/0 without the density of 11/0.
11/0: approximately 2 to 2.2mm diameter, roughly 18 to 20 beads per inch. The default size for the overwhelming majority of published bead weaving patterns, peyote, brick stitch, and loom work, which is why most beaders' stash and most pattern instructions are built around this size specifically.
12/0: approximately 1.8 to 1.9mm diameter, about 20 to 22 beads per inch. Uncommon and mostly seen in Czech seed bead lines, used as a middle step between 11/0 and 13/0/15/0 for fine detail work.
13/0 (charlottes and true cuts): approximately 1.6 to 1.7mm diameter. True cut charlottes have a single facet cut into each bead that catches light, prized for antique-style embroidery and edging rather than for structural weaving.
15/0: approximately 1.5mm diameter, roughly 24 to 25 beads per inch. The standard size for fine detail work, embroidery accents, and edging on peyote and other woven pieces where 11/0 would look too coarse.
18/0 (petite): approximately 1mm diameter. Rare, expensive relative to its size, and used almost exclusively for the finest embroidery and miniature work, since most bead weaving techniques become impractically slow at this scale by hand.
Cylinder beads are sized differently from round seed beads
Delica beads (Miyuki's cylinder bead line, also made by Toho as Treasures and Aiko) use the same aught numbers as round seed beads but describe a completely different shape: a perfect cylinder with thin walls and a large hole relative to the bead's size, rather than a rounded doughnut. An 11/0 Delica is not the same size or shape as an 11/0 round seed bead, and the two should not be substituted freely in a pattern written for one or the other, since cylinder beads sit flatter and tighter against each other, which is exactly why patterns with fine pixel-art-style detail specify Delicas by name.
Cylinder beads are more uniform bead to bead than round seed beads because the cutting process that makes them is more precise, which is the main reason serious bead weavers reach for Delicas on projects where a single oversized or undersized bead would visibly throw off a row.
Matching needle, thread, and wire to bead size
Needle size should generally exceed the bead's aught number: a size 12 or 13 beading needle passes through 11/0 and 15/0 seed beads comfortably, while a size 10 needle is the largest that reliably fits through 11/0 beads more than once or twice without binding. For 15/0 and smaller, many experienced beaders switch to a size 13 or 15 needle, or thread the beads directly onto stiff beading wire without a needle at all.
For stringing rather than weaving, beading wire diameter should leave comfortable clearance inside the bead hole: .014 inch wire suits most 11/0 and larger seed beads for multiple passes, while .010 or thinner wire is safer for 15/0 and smaller beads or for any design passing wire through the same bead several times. Thread choice for woven work, most commonly a nylon or fluorocarbon beading thread like Nymo, FireLine, or One-G, matters less for size compatibility than for strength and abrasion resistance, since thread flexes to fit where wire does not.