A chart says 1,200 beads. Nobody at the shop sells you twelve hundred; they sell you a tube. The gap between the two is a table — the app's beads-per-gram table, sourced across the brands (Miyuki, Toho, Delica, pony, fuse) — and the browser version of it lives in the shopping builder's bead-math tool.
Delica 11/0 run about 200 beads to the gram and sell in 7.2 g tubes — so a 1,200-bead chart color is 6 grams of beads; with the 10% spare, 6.6 g: one tube, with a little more than nothing left over. Miyuki's round 11/0 are heavier for their size: 110 per gram in an 8.5 g tube — the same shape of chart, a different answer. Ponies run 3.5 per gram in 22 g bags.
Type any count into the tool and it answers in the units the shop uses; the 10% spare is already the default, the same one the app's Shopping tab adds.
A beads-per-guess costs either a second tube or a week's delay. The table is the brands' own counts, and the tool carries the arithmetic next to the answer so you can check it while you buy.
Count what you own, order what you don't, and string something this week. — the bench crew