Timestamp Converter

About the Timestamp Converter

A Unix timestamp is the number of seconds that have elapsed since the Unix epoch, defined as 1970-01-01T00:00:00Z (UTC), excluding leap seconds. Because it is a single integer with no timezone, no locale, and no formatting ambiguity, it is the lingua franca for time in software — the format you will find in REST API responses, database columns, log files, message queues, and cron schedules. This converter translates a Unix timestamp into a human-readable date and back, in both directions, entirely in your browser.

How it works

The tool reads an integer and decides whether it is in seconds or milliseconds. Classic Unix time and MySQL's TIMESTAMP store seconds (a 10-digit number around 2020–2030), while JavaScript's Date.getTime() and Java's Instant use milliseconds (a 13-digit number). Feeding a 13-digit value where seconds are expected shifts the date by roughly 31,000 years, so the converter auto-detects magnitude by digit length and chooses the right unit. Internally it delegates to the browser's Date object, which represents every instant as a millisecond count from the epoch.

Two subtleties matter. First, the timestamp itself is always UTC; only the way you format it into year/month/day depends on a timezone. The same instant produces the same numeric timestamp in Seoul, London, and New York — what differs is the wall-clock string you render from it. Second, Unix time deliberately excludes leap seconds, so each UTC day is treated as exactly 86,400 seconds and the count advances linearly. The converter also accepts fractional seconds and emits ISO 8601 (YYYY-MM-DDTHH:mm:ss.sssZ) for round-tripping into any other system.

Common use cases

• Decoding a 10- or 13-digit timestamp from an API response into a local time
• Encoding a chosen date and time back into a Unix value for storage
• Comparing two instants across timezones by their UTC timestamp
• Debugging off-by-1000 bugs caused by mixing seconds and milliseconds
• Generating exp or iat claims for short-lived tokens

Worked example

The Unix timestamp 1717200000 converts to the ISO 8601 instant:

2024-06-01T04:00:00.000Z

Converting it back is lossless — parsing that ISO string with the browser's Date object returns exactly 1717200000. Because the Z suffix pins the value to UTC, the round-trip is independent of the viewer's local timezone. If you instead used 1717200000000 (13 digits, milliseconds) the same logic yields the identical instant; only the assumed unit changes.