Is epoch time in ms the same as Unix timestamp?

It uses the same epoch, but the unit is milliseconds instead of seconds. Classic Unix timestamp usually means seconds.

How many digits is an epoch millisecond timestamp?

For current dates, epoch milliseconds are usually 13 digits.

Does JavaScript use milliseconds or seconds?

JavaScript Date uses milliseconds. Date.now() returns epoch milliseconds.

How do I convert a Java long timestamp to a date?

If the long is epoch milliseconds, use Instant.ofEpochMilli(value); if it is epoch seconds, use Instant.ofEpochSecond(value). Check the digit count first — 13 digits is usually milliseconds, 10 digits is usually seconds.

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epoch 毫秒轉日期:轉換 13 位時間戳和 long 值

By unixepochtime.com editorial team2026年5月19日Updated 2026年6月29日

把 epoch 毫秒轉換為可讀日期的指南。涵蓋 13 位時間戳、JavaScript Date、Java long 值、毫秒與秒,以及為什麼錯誤的單位會產生 1970 年或很遙遠的日期。

什麼是 epoch 毫秒

epoch 毫秒計數自 1970 年 1 月 1 日 00:00:00 UTC 起的毫秒。它使用與 Unix 秒相同的 Unix 紀元,但精度多三位。現代的 epoch 毫秒值通常為 13 位,如 1700000000000。

如何把 millis 轉為日期

如果值已經是毫秒,JavaScript Date 可以直接讀取。如果接收工具期望秒,請先除以 1000。主要錯誤是在錯誤的邊界上做乘除。

JavaScript: new Date(1700000000000).toISOString()
Milliseconds to seconds: Math.floor(1700000000000 / 1000)
Seconds to milliseconds: 1700000000 * 1000
Java Instant: Instant.ofEpochMilli(1700000000000L)
Python: datetime.fromtimestamp(ms / 1000, tz=timezone.utc)

在 Java 與資料庫中把 long 轉為日期

搜尋「long 轉日期」通常來自 Java、Kotlin、Android,或把時間戳存為 64 位整數的資料庫匯出。該值可能是 epoch 毫秒,但也可能是秒、微秒或奈秒。轉換前請檢查位數。

10 位:很可能是 Unix 秒
13 位:很可能是 Unix 毫秒或 Java long 毫秒
16 位:很可能是微秒
19 位:很可能是奈秒
始終用單位命名欄位,例如 created_at_ms

為什麼毫秒會轉換成奇怪的日期

把毫秒值當作秒會得到極其遙遠的未來日期。把秒值當作毫秒會得到接近 1970 年 1 月的日期。位數是最快的診斷方式。

1700000000000 作為毫秒 = 2023-11-14 22:13:20 UTC
1700000000000 作為秒 = 約西元 55840 年,視函式庫而定
1700000000 作為秒 = 2023-11-14 22:13:20 UTC
1700000000 作為毫秒 = 1970-01-20 16:13:20 UTC

epoch 毫秒常見問題

A milliseconds value treated as seconds becomes an extremely far-future date. A seconds value treated as milliseconds becomes a date near January 1970. The digits are the quickest diagnostic.

1700000000000 as milliseconds = 2023-11-14 22:13:20 UTC
1700000000000 as seconds = year 55840 range, depending on the library
1700000000 as seconds = 2023-11-14 22:13:20 UTC
1700000000 as milliseconds = 1970-01-20 16:13:20 UTC

Cross-language patterns for ms-to-date

The conversion is structurally the same in every language — divide by 1000 (carefully) or use a millisecond-aware constructor. The details that bite are precision loss and naming.

JavaScript: new Date(1700000000000) — no division needed, Date is millisecond-based
Python: datetime.fromtimestamp(1700000000000 / 1000, tz=timezone.utc) — float division, watch for precision loss
Java: Instant.ofEpochMilli(1700000000000L) — exact millisecond precision preserved
PostgreSQL: SELECT to_timestamp(1700000000000.0 / 1000) — to_timestamp expects seconds, not milliseconds
SQLite: SELECT datetime(1700000000000 / 1000, 'unixepoch') — integer division drops fractional seconds
Go: time.UnixMilli(1700000000000) — added in Go 1.17 specifically to avoid the seconds-vs-ms mix-up
Ruby: Time.at(0, 1700000000000, :millisecond) for exact ms precision
C#: DateTimeOffset.FromUnixTimeMilliseconds(1700000000000L).UtcDateTime

FAQ

Is epoch time in ms the same as Unix timestamp?: It uses the same epoch, but the unit is milliseconds instead of seconds. Classic Unix timestamp usually means seconds.
How many digits is an epoch millisecond timestamp?: For current dates, epoch milliseconds are usually 13 digits.
Does JavaScript use milliseconds or seconds?: JavaScript Date uses milliseconds. Date.now() returns epoch milliseconds.
How do I convert a Java long timestamp to a date?: If the long is epoch milliseconds, use Instant.ofEpochMilli(value); if it is epoch seconds, use Instant.ofEpochSecond(value). Check the digit count first — 13 digits is usually milliseconds, 10 digits is usually seconds.