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ミリ秒から日時に変換

JavaScriptなどで標準的な13桁のエポックミリ秒を日時に変換します。

Milliseconds → date & time

13 digits is typical today; fractional values are rounded to the nearest millisecond.

仕組みと計算ルール

  1. Epoch milliseconds count milliseconds since 1970-01-01T00:00:00Z, the unit used by Java, JavaScript, .NET and most web APIs. A current value has 13 digits (≈ 1.7 × 10¹²).
  2. The value is rounded to the nearest whole millisecond when it has a fraction (JavaScript Date precision is 1 ms), then decoded to an exact UTC instant.
  3. The same instant is shown in UTC and your local zone, plus the equivalent 10-digit epoch seconds for cross-checking.

知っておくと便利なポイント

  • This page always reads input as milliseconds. A 10-digit value like 1700000000 is seconds; feeding it here produces a 1970-era date. Use the Unix Timestamp Converter when the unit is uncertain.
  • UTC and local dates can differ by a day around midnight; both are shown to make that visible instead of surprising.
  • The full JavaScript Date range (±8.64×10¹⁵ ms) is supported; beyond it the value is rejected with an explanation.
タイムスタンプツール

Unixタイムスタンプから日時に変換

数値をUTCおよびお使いの端末の現地時刻の日付・時刻に変換します。

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タイムスタンプツールおすすめ

Unixタイムスタンプ相互変換

タイムスタンプを日時に、日時を秒・ミリ秒のタイムスタンプに変換します。

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タイムスタンプツール

ISO 8601変換

日時を国際標準ISO 8601形式の文字列に変換・解析します。

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タイムスタンプツール

UTCタイムスタンプ変換

タイムスタンプを時差なしの純粋なUTC日時に直結して変換します。

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よくある質問

Which systems use millisecond timestamps?
Java, JavaScript, .NET, and most web APIs and log formats. If your value has 13 digits and is around 1.7 trillion, it is almost certainly milliseconds.
Can I enter fractional milliseconds?
You can enter decimals, and the tool rounds to whole milliseconds explicitly. JavaScript Date precision is one millisecond, so finer detail cannot be represented.
Why is the result a day off from my log’s date?
Log viewers often show UTC while you expect local time (or vice versa). The converter shows both UTC and your local zone so the discrepancy is visible instead of confusing.