Timestamp Converter

What the Timestamp Converter Does

It works both directions. Type a Unix timestamp and you immediately see three readings — the UTC date and time, the same moment in your device's local timezone, and the ISO 8601 string — so you can read an epoch value from a log or an API. Pick a date and time and it returns the matching Unix value in both seconds and milliseconds.

A current-time button fills in the present moment, which is handy for grabbing a timestamp to drop into code or a test. Everything updates as you type.

How It Works

Unix time is the number of seconds since the epoch — midnight UTC on 1 January 1970 — so the tool turns a timestamp into a date by counting that many seconds forward. It detects the unit by length: a value of ten digits or fewer is read as seconds, and a longer one as milliseconds, since a seconds value passed the ten-digit mark only recently and milliseconds values are three digits longer.

The UTC reading is the unambiguous one; the local reading applies your device's timezone offset to the same instant; and the ISO 8601 string is the standard machine-readable format. Converting the other way, a chosen date is expressed as whole seconds (rounded down) and as milliseconds.

Data source & conversion logic

1. Read the value. Take the timestamp, or the chosen date and time.
2. Detect seconds or milliseconds. Treat a value of ten digits or fewer as seconds; a longer one as milliseconds.
3. Convert to the instant. Count that many seconds (or milliseconds) from the 1970 UTC epoch.
4. Show the readings. Display UTC, local time and ISO 8601 — or, for a date, the Unix seconds and milliseconds.

Unix time

The tool reads ten digits or fewer as seconds and longer values as milliseconds.

Technical Details

Standards & references

• Unix epoch — Unix time counts seconds since 00:00:00 UTC on 1 January 1970, not counting leap seconds; it is the timekeeping basis for most computer systems.
• Seconds vs milliseconds — a ten-digit value is normally seconds; a thirteen-digit value is milliseconds (a thousand times larger). The tool picks the unit by length.
• ISO 8601 — the international date-time format (such as 1970-01-01T00:00:00Z) that this tool also outputs, designed to be unambiguous across systems.

Accuracy & Limitations

It detects seconds versus milliseconds by the number of digits — ten or fewer means seconds. That is right for almost all timestamps today, but an unusual value can fool it: a milliseconds value from the early 1970s has few digits and would be misread as seconds, and a seconds value beyond the year 2286 has eleven digits and would be misread as milliseconds.

The local reading depends on your device's timezone and clock. The same instant shows a different wall-clock time on a machine set to another zone; the UTC and ISO readings are the ones that are the same everywhere.

Unix time ignores leap seconds, by definition. It is a count of seconds since 1970 as if every day were exactly 86,400 seconds, so it can differ by a handful of seconds from strict astronomical time — which is intentional and standard.

This is a browser tool using 64-bit dates, so the famous Year 2038 problem does not affect it. That bug hits systems that store Unix time in a signed 32-bit integer, which overflows in January 2038; browsers handle dates far beyond that.

Whole seconds are rounded down. Converting a date that includes a fractional part to seconds truncates rather than rounds, so the seconds value is the floor of the exact time.

Real-World Use Cases

When to use it — and when not to

Need the gap between two dates? Use a date-difference calculator. Converting between named time zones (not just UTC and local)? A world-clock or timezone tool handles that. Working with durations? A time-duration calculator fits better.

Frequently Asked Questions

References

• Unix time (Wikipedia)
• Year 2038 problem (Wikipedia)
• Date (MDN Web Docs)

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