Avery 48660 — 30 per sheet. For correct alignment, in your browser's print dialog set Scale: 100% (or "Actual size" — not "Fit to page"), Margins: Default, and Paper: US Letter.
Printer alignment (optional)
Only needed if labels still sit a little high/low or left/right on your specific printer — after you've confirmed Scale is 100%. This shifts the whole sheet and is saved on this device.
Farm