How big is a zettabyte, and where does it sit in the sequence of data-size units?

A zettabyte is 1000⁷ bytes (10²¹) — the scale humanity's total digital data now lives at.

Each step up multiplies by 1000 (using the decimal SI convention):

Byte → KB → MB → GB → TB → PB → EB → ZB → YB → RB → QB

• Kilobyte (KB) = 1000¹
• Megabyte (MB) = 1000²
• Gigabyte (GB) = 1000³
• Terabyte (TB) = 1000⁴
• Petabyte (PB) = 1000⁵
• Exabyte (EB) = 1000⁶
• Zettabyte (ZB) = 1000⁷
• Yottabyte, Ronnabyte, Quettabyte = 1000⁸ ⁹ ¹⁰

Gotcha: marketing/SI units are powers of 1000; the binary units your OS often reports (KiB, MiB, GiB) are powers of 1024. A "1 TB" disk shows up as ~0.91 TiB for exactly this reason.