Seconds vs milliseconds
A 10-digit Unix timestamp is usually seconds. A 13-digit timestamp is usually milliseconds. Mixing them creates dates that look wildly wrong.
Guide
Unix Timestamp to Local Time
Unix timestamps are common in logs, APIs, and databases. This guide explains seconds vs milliseconds and how to convert epoch values to local time zones.
UTC
Universal · UTC
12:56 PM
Sun, Jul 26
±0h
🟢 Working
Mumbai
India · Asia/Kolkata
6:26 PM
Sun, Jul 26
+5h30m
🌆 Evening
New York
USA · America/New York
8:56 AM
Sun, Jul 26
-4h
🌅 Early morning
London
UK · Europe/London
1:56 PM
Sun, Jul 26
+1h
🟢 Working
Quick answer
Key takeaways
- Unix timestamps count time from 1970-01-01 00:00:00 UTC.
- Some systems use seconds and others use milliseconds.
- Store timestamps in UTC, then display them in the user local time zone.
UTC first, local display later
Most systems store timestamps in UTC. Convert to local time only for display, reports, customer support, or human scheduling.
Debugging logs
When comparing logs across servers, convert every timestamp from UTC into the same target zone before comparing event order.
Developer examples
Code examples for epoch time conversion
Copy a snippet and replace the timestamp or time zone with the values you need.
JavaScript
Convert epoch seconds to India time in the browser or Node.js.
const epochSeconds = 1700000000;
const date = new Date(epochSeconds * 1000);
console.log(date.toLocaleString('en-US', {
timeZone: 'Asia/Kolkata',
dateStyle: 'medium',
timeStyle: 'long',
}));Python
Convert a Unix timestamp from UTC into a local IANA time zone.
from datetime import datetime, timezone
from zoneinfo import ZoneInfo
epoch_seconds = 1700000000
utc_time = datetime.fromtimestamp(epoch_seconds, tz=timezone.utc)
local_time = utc_time.astimezone(ZoneInfo("Asia/Kolkata"))
print(local_time.isoformat())Java
Use java.time to convert epoch seconds into a ZonedDateTime.
import java.time.Instant;
import java.time.ZoneId;
import java.time.ZonedDateTime;
Instant instant = Instant.ofEpochSecond(1700000000L);
ZonedDateTime localTime = instant.atZone(ZoneId.of("Asia/Kolkata"));
System.out.println(localTime);PostgreSQL
Convert epoch seconds to a local timestamp inside a query.
SELECT
to_timestamp(1700000000) AT TIME ZONE 'Asia/Kolkata'
AS india_time;Terminal
Check an epoch value from macOS/BSD or Linux/GNU date.
# macOS / BSD
TZ=Asia/Kolkata date -r 1700000000
# Linux / GNU
TZ=Asia/Kolkata date -d @1700000000Frequently Asked Questions
What is Unix time?
Unix time is the number of seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds in most systems.
How do I know if a timestamp is seconds or milliseconds?
10 digits usually means seconds. 13 digits usually means milliseconds.
How do I convert epoch time in code?
Use the timestamp as UTC first, then format it with an IANA time zone such as Asia/Kolkata, America/New_York, or Europe/London.
Should timestamps be stored in local time?
Usually no. Store in UTC and convert for display.