Timestamp Converter

What the Timestamp Converter does

It works in both directions. Type a Unix timestamp and you see three readings of it: the UTC date and time, the same moment in your device's timezone, and the ISO 8601 string. That makes an epoch value from a log or an API easy to read. Pick a date and time and you get the matching Unix value in seconds and in milliseconds.

A current-time button fills in the present moment, handy when you need a timestamp for 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 decides the unit by length. Ten digits or fewer is read as seconds, and anything longer as milliseconds, because millisecond values are three digits longer and seconds values only recently reached ten digits.

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 form. Going the other way, a chosen date comes out 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 and references

• Unix epoch: Unix time counts seconds since 00:00:00 UTC on 1 January 1970, not counting leap seconds. Most computer systems keep time this way.
• Seconds vs milliseconds: A ten-digit value is normally seconds and 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. The tool outputs it too, because it reads the same on every system.

Accuracy and limits

It tells seconds from milliseconds by the number of digits: ten or fewer means seconds. That's right for almost every timestamp in use today, but an odd value can fool it. A milliseconds value from the early 1970s has few digits and would be read as seconds, and a seconds value after the year 2286 has eleven digits and would be read as milliseconds.

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

Unix time ignores leap seconds by definition. It counts as if every day had exactly 86,400 seconds, so it can drift a few seconds from strict astronomical time. That's intended, and every system that uses Unix time does the same.

The tool runs on the browser's 64-bit dates, so the Year 2038 problem doesn't 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. A date with a fractional second is truncated, so the seconds value is the floor of the exact time.

Real-world uses

When it fits, and when it doesn't

Need the gap between two dates? Use a date-difference calculator. For converting between named time zones, not just UTC and local, a world-clock or timezone tool does the job, and durations belong in a time-duration calculator.

Frequently asked questions

References

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

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