Unix Timestamp: 10 Digits or 13? Seconds vs Milliseconds

The two flavors

A Unix timestamp counts seconds (or milliseconds) since 1970-01-01T00:00:00Z.

Unit	Digits (now)	Example
Seconds	10	1780000000
Milliseconds	13	1780000000000

The bug

Code that expects seconds but gets milliseconds (or the reverse) is wrong by exactly 1000×:

const exp = 1780000000;          // seconds (JWT-style)
const now = Date.now();          // milliseconds
// WRONG: compares ms to seconds
if (now > exp) { /* always true */ }

// RIGHT: same unit
if (Math.floor(now / 1000) > exp) { /* correct */ }

How to tell which you have

• 10 digits → seconds.
• 13 digits → milliseconds.
• If a “timestamp” is 1.78e12, it is milliseconds.

Convert

const sec = Math.floor(Date.now() / 1000);     // ms -> s
const ms  = sec * 1000;                         // s -> ms

Watch JWT and databases

• JWT exp/iat/nbf are seconds.
• JavaScript Date.now() is milliseconds.
• SQL FROM_UNIXTIME() usually expects seconds; unix_timestamp() returns seconds.

Convert any value

Paste a timestamp and see the date in both units with the Timestamp Converter on Toolbox.

Related tools

• Timestamp Converter on Toolbox
• Timestamp Converter on Toolhub
• Timestamp Converter on DevTools
• Epoch Converter on DevTools

Next steps

• JWT claims use these seconds — see JWT signature verification failed.
• Sortable IDs also lean on time — UUID vs ULID.