Establish the unit before converting
Two log systems may describe the same instant with different numbers. The Unix Timestamp Converter offers explicit Unix seconds, Unix milliseconds, and ISO date modes so that you can state which representation you have. Do not choose a unit solely by the number’s length when the producing system documents it.
Paste the number or date into Timestamp or ISO date with a time zone, select the corresponding Input format, and process it. The result includes an ISO UTC value, Unix seconds, Unix milliseconds, and a display using the browser’s local time zone.
Convert a known instant
Enter 1700000000 and select Unix seconds. The expected fields include:
{
"iso": "2023-11-14T22:13:20.000Z",
"unixSeconds": 1700000000,
"unixMilliseconds": 1700000000000
}The local field varies with your browser’s configured zone. Now enter 1700000000000 in Unix milliseconds mode. You should recover the same UTC ISO value. If you enter the first number as milliseconds instead, the result describes a different instant near the start of 1970; that mismatch is a useful clue when diagnosing a unit error.
Include the offset in ISO input
For ISO date mode, supply a date-time with Z or a numeric UTC offset, such as 2023-11-14T22:13:20Z. A bare wall-clock value like 2023-11-14T22:13:20 is rejected because its zone is unspecified. An offset states the relationship to UTC for that instant; it does not encode a location’s future daylight-saving rules.
Use Time Zone Converter when your starting point is a local date and time in a named IANA zone. That tool can distinguish a normal wall time from one occurring around a clock change. For a JWT timing claim, consult its producer’s format and use seconds when appropriate; JWT Decoder exposes claims without verifying them.
Read precision and privacy limits
The ISO output is based on JavaScript Date precision in milliseconds. The seconds field is rounded down with Math.floor, so a fractional instant is not represented as fractional seconds in that field. Dates outside the supported browser range produce an error rather than a usable result.
Conversion happens in your browser. A timestamp can still reveal activity when combined with a user identifier or log message, so use a representative example when sharing diagnostics. Preserve the original log entry beside the converted value to keep the source unit and context reviewable.