Published by SOPIDOTECH LTD · · 3 min read

A timestamp from an API can look wrong simply because seconds were interpreted as milliseconds. Choose the unit before interpreting the date.

Open the Unix Timestamp Converter to follow the workflow. Processing runs in your browser; the tool does not upload the input for conversion.

A practical workflow

  1. Choose conversion direction. Select Timestamp to date or ISO date to timestamp.
  2. Set the unit and display timezone. Choose seconds or milliseconds, then a timezone such as UTC or Africa/Lagos.
  3. Run and compare representations. Review ISO UTC, seconds, milliseconds and the selected timezone display.
  4. Copy or download the result. Use the representation expected by your API or database.

Try a concrete example

The following demonstration input is also available in the workspace. Replace it with your own data after checking the expected behaviour.

1791878400

With the default settings, the result is:

{
  "iso": "2026-10-13T08:00:00.000Z",
  "seconds": 1791878400,
  "milliseconds": 1791878400000,
  "local": "Tuesday, 13 October 2026 at 08:00:00 UTC",
  "zone": "UTC"
}

Distinguish seconds from milliseconds

A value of 1000 seconds is an instant more than sixteen minutes after the epoch; 1000 milliseconds is one second after it. The tool does not guess the unit from digit count. Select it explicitly and inspect both numeric representations in the result.

Use an explicit timezone in date input

ISO input needs Z for UTC or a numeric offset such as +01:00. A local date without that information is ambiguous, so it is rejected. The display timezone changes the human-readable representation of the instant, not the underlying Unix value.

Check date validity and precision

Calendar dates and time components are checked before conversion. Negative timestamps describe instants before the epoch. Extremely large values or unsafe integers are rejected. Ordinary Unix time does not count leap seconds as separate timestamp values.

If the result needs attention

Date input must include Z or a numeric offset. Timezone display does not change the Unix instant. Invalid or out-of-range values are rejected.

Read the exact error before changing the input. Keep a copy of the original, reduce the sample when investigating a large file, and use the destination application to verify that the result has the meaning you intended. The tool processes the supplied data; it cannot infer an unstated application schema or project requirement.

Use the Text Diff Checker to compare a saved result with the original. Keep transformation and application testing as separate steps so presentation changes are not mistaken for verified behaviour.

Sources and further reading

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