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What is a Unix Timestamp?

A Unix timestamp (also known as Unix time, POSIX time, or Epoch time) is a system for describing a point in time. It is the number of seconds that have elapsed since the Unix epoch, which was at 00:00:00 UTC on 1 January 1970.

Because it's a single, universally consistent number, it's not affected by timezones, making it ideal for use in computer systems and data storage worldwide.

Common Use Cases

• Storing dates in databases: Using a single integer is efficient and avoids timezone-related bugs.
• APIs and Web Services: Many APIs use timestamps to represent dates for data exchange between systems.
• Logging and Timestamps: Recording event times in log files with a consistent format.
• Caching: Setting expiration times for cached data (e.g., in Redis or Memcached).

How It Works

The concept is simple: we count the number of seconds from a fixed starting point, the 'epoch'. This tool converts that count back into a human-readable date, or vice-versa.

When converting to a date, you must select the correct timezone to ensure the date and time are displayed accurately for that location.

Seconds vs. Milliseconds

Traditionally, Unix time is in seconds. However, many modern systems and programming languages (like JavaScript) work with milliseconds to achieve higher precision. A millisecond timestamp is simply the number of milliseconds since the epoch.

This tool automatically detects whether your input is in seconds (a 10-digit number) or milliseconds (a 13-digit number) and handles the conversion correctly.

The Importance of Timezones

A timestamp itself is just a number without a timezone. It represents the same moment in time everywhere. However, to display it as a human-readable date (e.g., 'March 15th, 2:00 PM'), we must know *where* in the world we are.

For example, a single timestamp corresponds to 9 AM in Tokyo (UTC+9) but 5 PM the previous day in Los Angeles (UTC-7). Selecting the correct timezone is crucial for accurate representation.