Timestamp converter
Convert Unix seconds/milliseconds to local time, UTC, ISO 8601, RFC 2822, Excel serial numbers and Mongo ObjectId timestamps, with automatic seconds/milliseconds detection.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Current timestamp
Local time uses your browser time zone; Excel serial numbers start at 1899-12-30 (including the 1900 leap year bug).
————Result
Date to timestamp
Accepts ISO 8601, RFC 3339, RFC 2822 and YYYY-MM-DD HH:mm:ss; strings without a time zone are read as UTC
What this tool does
- Turn a bare number like 1700000000 into a real date: seconds and milliseconds are detected automatically and you see local time, UTC and ISO 8601 at once.
- Debug time zone problems: local time is shown with an explicit offset such as +08:00 next to the UTC time, so the gap is obvious.
- Integrate with other systems: get RFC 2822 (email header format), the Excel serial number (starting 1899-12-30) and the Mongo ObjectId time prefix in the same view.
- Works in reverse too — convert a string such as 2026-10-10 12:00:00 into Unix seconds and milliseconds.
Example
Input
1700000000 (auto-detected as seconds)
Output
Local time: 2023-11-15 06:13:20 +08:00 UTC time: 2023-11-14 22:13:20 UTC ISO 8601: 2023-11-14T22:13:20.000Z RFC 2822: Wed, 15 Nov 2023 06:13:20 +0800 Excel serial: 45244.92592592593 Mongo ObjectId prefix: 6553f100 Unix seconds: 1700000000 Unix milliseconds: 1700000000000
The local time above assumes UTC+8; your browser uses your own time zone, so that line may differ.
Frequently asked questions
How are 10-digit and 13-digit values told apart?
Auto-detection counts digits: 1–10 digits are read as seconds and 11–13 as milliseconds. So 1700000000 is 2023-11-15, while 1700000000000 is the same instant written in milliseconds. Switch the unit selector to seconds or milliseconds if the guess is wrong.
Why do local time and UTC differ by several hours?
Local time applies your browser's time zone offset, while UTC is pinned to offset 0. Both lines describe the same instant, just rendered for different places — which is why the local line carries a suffix such as +08:00.
Why does the Excel serial number have decimals?
Excel stores a date as the number of days since 1899-12-30, and the fractional part is the time of day. 1970-01-01 maps to 25569, so 2023-11-15 06:13:20 becomes 45244.925…, which Excel renders as a date once the cell is formatted as one.
What happens if a date string has no time zone?
A value such as 2026-10-10 12:00:00 is parsed as UTC and yields 1791633600. For local time, write an ISO 8601 string with an offset, for example 2026-10-10T12:00:00+08:00.
Is the timestamp sent anywhere for validation?
No. Parsing and formatting happen entirely in your browser, and the "current timestamp" is just a local Date.now(); the page makes no requests.
Keywords：timestampunixepoch时间戳毫秒秒iso 8601rfc 2822excel serialobjectidunix 时间戳转换