Seed bead size chart and substitution calculator

Sizes are written in aughts — 15/0, 11/0, 8/0, 6/0 — counting roughly how many beads fit in an inch, so the number grows as the bead shrinks. Diameter is the bead measured across the hole; spacing is how much width a bead actually takes in a row, which is smaller because beads nest against each other. The substitution figure keeps the row width and divides it by the new bead's spacing, so a pattern moved into a narrower bead gains beads and keeps its finished size — but the chart has to be redrawn to that new cell count.

Example: swapping 20 Preciosa 10/0 for Miyuki Delica 11/0
A 20-bead row in Preciosa 10/0 is about 3.5 cm wide. Keeping that width in Miyuki Delica 11/0 takes 27 beads, so the chart has to be redrawn about a third wider in cells.

6/0, at roughly 4 mm, then 8/0 around 3 mm, 11/0 around 2.1 mm, and 15/0 at about 1.5 mm. The size number counts beads per inch, so it rises as the bead gets smaller.

No. Delica is a cylinder bead: 11/0 Delica is about 1.6 mm across with straight walls, while a round 11/0 is about 2 mm. They are not interchangeable inside the same row.

Yes, if you accept one of two changes. The same number of beads in a smaller size makes a smaller piece; the same finished size needs more beads and a redrawn chart.