Convert Unix timestamps and explicit time zones

Understand the settings

A Unix timestamp measures elapsed time from the Unix epoch. APIs may store it in seconds or milliseconds, and confusing those scales produces very different dates. Select the unit explicitly instead of judging only by how many digits you see.

UTC represents a common reference. Local display uses your browser’s time zone and its time-zone rules. Two people can view the same instant with different clock readings. A date-time string without an offset can be ambiguous, so the converter expects a clear ISO date-time with Z or an explicit offset.

Civil-time changes can create repeated or missing local clock times. This tool converts instants; it does not decide which occurrence a person intended during a daylight-saving transition. Keep an offset in machine-readable timestamps when exchanging logs.

Step by step

1. Choose seconds or milliseconds and enter a Unix value.
2. Convert to inspect UTC and local representations.
3. For the reverse direction, enter an ISO date-time with Z or an explicit offset.
4. Check calendar validity and the selected scale before copying the result.

Start at the epoch

Unix value 0 represents 1970-01-01T00:00:00.000Z. A local display may show the previous evening west of UTC. That is the same instant, not an off-by-one-day error.

Limits and what to check

• Uses browser date/time facilities, with millisecond precision and their supported date range.
• No leap-second scheduling, astronomical time conversion or timezone-database editor.
• Invalid calendar dates are rejected rather than silently normalized.
• No input is uploaded. Local time reflects the device/browser configuration.

Troubleshooting