“Your API response is full of numbers like 1700000000 - what time is that?” or “how do I read an epoch timestamp?” - these are moments when Unix time conversion helps.
In this article, we explain how to convert Unix time (epoch timestamps) to dates, covering seconds vs milliseconds, timezone handling, and where developers use it.
What is Unix time?
Unix time (epoch time) represents a moment as the number of seconds since January 1, 1970, 00:00:00 UTC. It is widely used in programs and APIs.
1700000000 → November 15, 2023, 06:13:20 UTC- Positive values: after 1970
- Negative values: before 1969
- Integers make comparisons and arithmetic trivial
Key point: Unix time is always UTC-based. Timezones only matter when you display it - your browser converts to local time.
Seconds vs milliseconds (10 vs 13 digits)
Unix time appears in two forms:
| Digits | Unit | Example | Meaning |
|---|---|---|---|
| 10 digits | seconds | 1700000000 |
seconds since 1970 |
| 13 digits | milliseconds | 1700000000000 |
milliseconds since 1970 |
13 digits are exactly 1000× the 10-digit value. JavaScript’s Date.now() returns 13 digits (ms); PHP’s time() returns 10 digits (seconds).
Converting between them
- 13 → 10 digits: divide by 1000 (
1700000000000 ÷ 1000 = 1700000000) - 10 → 13 digits: multiply by 1000 (
1700000000 × 1000 = 1700000000000)
Timezones
Unix time has no timezone - the same value is the same moment worldwide. You convert it to a local timezone only when displaying:
- Tokyo (JST) = UTC + 9 hours
- New York (EST) = UTC − 5 hours (standard time)
Example: 1700000000 (UTC 06:13:20)
- Tokyo: 15:13:20
- London (UTC): 06:13:20
- New York (EST): 01:13:20
Caution: Reading a 10-digit value as milliseconds snaps the date back to 1970. Always check the digit count.
Where developers use it
- API responses: many web APIs return timestamps as Unix time
- Databases: storing time as an integer simplifies comparisons
- Expiry checks: token and session expiration compared as numbers
- Log analysis: human-readable conversion for debugging
Practical example: reading an API log
Imagine a server log line like this:
2026-08-12T14:30:00+09:00 request failed, user_id=42, error_at=1754973000The error_at field is a Unix timestamp. To understand when the error happened:
- Count the digits - 10 digits means seconds
- Convert it with the Tools Hub converter to see both local time and UTC
- Compare it with other timestamps in the same log to measure delays
Being fluent with this conversion turns opaque numbers into readable dates in seconds, which is why every developer should have a converter handy.
How to convert Unix time
With the Tools Hub Unix time converter, both 10-digit and 13-digit values are converted to local time and UTC instantly.
Enter the timestamp
Paste a 10-digit (seconds) or 13-digit (milliseconds) value.
Read the datetime
Both your local time and UTC are displayed.
Convert in reverse too
The tool also converts a datetime back to Unix time.
The tool introduced in this article
Unix Time Converter
Converts 10- and 13-digit timestamps both ways. All in your browser.
Why timestamps beat formatted strings
Databases and APIs often store Unix time instead of date strings like “2026-08-12 14:30:00”. There are good reasons: integers compare instantly, they are timezone-independent, and they never suffer from locale formatting differences. The cost is readability - which is exactly why conversion tools exist. When you need to debug, report or display a value, convert it; when you store or transmit it, keep the integer. This division of labor is what most production systems rely on.
Summary
- Unix time = seconds since January 1, 1970, 00:00:00 UTC
- 10 digits = seconds, 13 digits = milliseconds (1000×)
- Timezones matter only when displaying (the value itself is UTC)
- Used constantly in APIs, databases and log analysis
- The Tools Hub converter handles it all in your browser
Next time you need to read a timestamp, use the steps above or the Tools Hub Unix time converter.
FAQ
What is Unix time?
A way of representing time as the number of seconds (or milliseconds) since January 1, 1970, 00:00:00 UTC. Widely used in programming and APIs.
What is the difference between 10 and 13 digits?
10 digits are seconds, 13 digits are milliseconds - exactly 1000× the value. JavaScript’s Date.now() returns 13 digits; PHP’s time() returns 10.
How do timezones work?
Unix time is UTC-based. To display in Japan time, add 9 hours. The converter shows both local time and UTC.
Can I convert a datetime back to Unix time?
Yes. The reverse conversion feature calculates the Unix time for any datetime you specify.
