How do I know if a timestamp is in seconds or milliseconds?

A 10-digit timestamp is in seconds (valid until year 2286). A 13-digit timestamp is in milliseconds. JavaScript's Date.now() and most browser APIs use milliseconds; Python's time.time() and Unix system calls use seconds (as a float); databases typically use seconds in INTEGER columns.

What is the Year 2038 Problem?

Signed 32-bit integers can store a maximum value of 2,147,483,647, which as a Unix timestamp corresponds to January 19, 2038 at 03:14:07 UTC. After that point, the integer overflows to negative, causing date calculations to produce incorrect results. Systems migrating from 32-bit to 64-bit timestamps (which won't overflow for billions of years) avoid this problem.

Why is Unix time measured from January 1, 1970?

The Unix operating system was developed at Bell Labs in the late 1960s and early 1970s. The developers chose January 1, 1970 as a convenient recent round-number starting point when defining the timekeeping system for Unix. The choice was somewhat arbitrary — the year 1900 and 1900 January 1 were other candidates discussed.

Unix Timestamp Converter | DevStackTools

Unix Timestamp Converter — Convert Epoch Time to Human-Readable Dates

Understanding the Basics

Unix time (also called POSIX time, Epoch time, or Unix timestamp) is a system for describing points in time, defined as the total count of seconds (or milliseconds in many programming contexts) that have elapsed since the Unix Epoch: 00:00:00 UTC on Thursday, 1 January 1970. This simple integer representation has become the universal way to store and compare timestamps in computer systems: it avoids timezone ambiguity (being absolute), works correctly across daylight saving time transitions, enables trivial arithmetic for computing durations and offsets, fits in a 32-bit integer (for seconds) or 64-bit integer (for milliseconds), and is supported natively by every programming language and database engine. In JavaScript, Date.now() returns milliseconds. In Python, time.time() returns seconds as a float. In SQL databases, Unix timestamps are commonly stored in BIGINT columns. In operating systems, file modification times, network packet timestamps, and process scheduling all use some form of Unix time. The "Year 2038 Problem" affects systems using signed 32-bit integers for Unix seconds — those values overflow on January 19, 2038 at 03:14:07 UTC, which is why 64-bit timestamps are now standard.

How to Use the Tool

To convert Timestamp → Date: enter a 10-digit Unix timestamp (seconds) or 13-digit timestamp (milliseconds) in the Timestamp field. The tool shows the UTC date, local date, and relative time ("3 hours ago").
To convert Date → Timestamp: use the date-time picker to select a specific date and time. The tool outputs the corresponding Unix timestamp in both seconds and milliseconds.
The "Now" button populates the current Unix timestamp for use as a reference point.
Timezone offset is shown next to the local date to clarify the difference from UTC.
Copy any result value directly to clipboard with the copy icon beside each output.

Key Features & Specifications

Bidirectional conversion: Unix timestamp ↔ human-readable date and time
Supports both 10-digit (seconds) and 13-digit (milliseconds) Unix timestamps
Shows UTC date, local date in your browser's timezone, and relative time
Date picker for converting a chosen date/time to its Unix timestamp
Displays timezone offset (e.g., UTC+5:30) for transparent local time conversion

Frequently Asked Questions (FAQ)

Q:How do I know if a timestamp is in seconds or milliseconds?: A 10-digit timestamp is in seconds (valid until year 2286). A 13-digit timestamp is in milliseconds. JavaScript's Date.now() and most browser APIs use milliseconds; Python's time.time() and Unix system calls use seconds (as a float); databases typically use seconds in INTEGER columns.
Q:What is the Year 2038 Problem?: Signed 32-bit integers can store a maximum value of 2,147,483,647, which as a Unix timestamp corresponds to January 19, 2038 at 03:14:07 UTC. After that point, the integer overflows to negative, causing date calculations to produce incorrect results. Systems migrating from 32-bit to 64-bit timestamps (which won't overflow for billions of years) avoid this problem.
Q:Why is Unix time measured from January 1, 1970?: The Unix operating system was developed at Bell Labs in the late 1960s and early 1970s. The developers chose January 1, 1970 as a convenient recent round-number starting point when defining the timekeeping system for Unix. The choice was somewhat arbitrary — the year 1900 and 1900 January 1 were other candidates discussed.