Unix timestamp converter

Software that stores Unix time in a signed 32-bit integer can count only to 2,147,483,647 seconds, reached at 03:14:07 UTC on 19 January 2038. One second later the value wraps to −2,147,483,648, which reads as 20:45:52 UTC on 13 December 1901. A signed 64-bit count, the usual size on current 64-bit systems, lasts about 292 billion years.

Count the digits. Present-day times have 10 digits in seconds, 13 in milliseconds, 16 in microseconds and 19 in nanoseconds; the seconds count reached 1,000,000,000 on 9 September 2001 and stays at 10 digits until 20 November 2286. JavaScript's Date.now() and Java's System.currentTimeMillis() return milliseconds, while the shell command date +%s and Python's time.time() return seconds.

No. POSIX defines every day as 86,400 seconds, so the 27 leap seconds added to UTC between 1972 and 2016 have no timestamps of their own, and 23:59:60 cannot be written as Unix time. Systems either repeat a second when one occurs or spread it out; Google, for example, smears a leap second over the 24 hours from noon to noon UTC.

Yes. A timestamp names one instant, and the zone only changes how that instant is written. Timestamp 0 is 00:00 UTC on 1 January 1970, which was 05:30 the same day in India, 19:00 on 31 December 1969 in New York, and 01:00 in London, where British Standard Time kept clocks on UTC+01:00 all year from 1968 to 1971.

Type now in the timestamp box, or ask the system clock: date +%s in a Linux or macOS shell, Math.floor(Date.now() / 1000) in JavaScript, int(time.time()) in Python, and SELECT UNIX_TIMESTAMP() in MySQL. The count grows by 86,400 a day and passes 1,800,000,000 at 08:00 UTC on 15 January 2027.

精度は入力値と計算方法の前提に依存します。十進演算には有効数字50桁を使いますが、推定、数値計算手法、元データの精度はそれより低い場合があります。表示の丸め処理でこれらの制約がなくなるわけではありません。 独立した出典の解答と照合した計算例：8。 例えば、「The epoch」はPOSIX definition; Python datetime.fromtimestamp(0, timezone.utc)と照合しています。

POSIX.1-2017, §4.16 Seconds Since the Epoch; ISO 8601-1:2019 — Date and time representations; IANA Time Zone Database.