A Unix timestamp is simply the number of seconds (or milliseconds) that have passed since midnight UTC on January 1, 1970 — the "Unix epoch." It's a single, unambiguous number regardless of timezone, which is exactly why it's so common in logs, APIs, and databases, but it's not human-readable on its own. This tool converts it into a readable date in any timezone you choose, shows relative time ("3 hours ago"), batch-converts a whole list at once, and outputs ISO 8601 and RFC 2822 formats.
The timestamp itself never changes — it's a fixed count of seconds since the epoch. What changes is how that fixed instant gets displayed, since 3pm in New York is the same moment as 8pm in London; the timezone selector just controls which local representation you're viewing.
ISO 8601 (like 2026-09-18T14:30:00Z) is the compact, sortable format used throughout modern APIs and databases. RFC 2822 (like Thu, 18 Sep 2026 14:30:00 +0000) is the older, more verbose format historically used in email headers and HTTP dates — both represent the same moment, just formatted for different systems.
Yes — a 10-digit number is typically seconds, while a 13-digit number (like from JavaScript's Date.now()) is milliseconds, and mixing them up gives a wildly wrong date. This converter detects and handles both, but it's worth knowing which one your source system actually uses if you're working with raw numbers elsewhere.