Timestamp Converter

How automatic seconds-vs-milliseconds detection actually works

With "Auto detect" selected, the tool only looks at the absolute value of the input: anything below 100,000,000,000 is treated as seconds, and anything at or above that threshold is treated as milliseconds. Entering 1735689600 (a seconds value near 2025) is read as seconds, while 1735689600000 (the same instant in milliseconds) is read as milliseconds, and both should convert to the same calendar day.

To verify the result, click "Use current time" to fill the field with the current instant and force the unit to milliseconds, then compare the local-time field on screen with your computer's system clock to confirm the conversion logic is working correctly.

• Input 1735689600 with Auto detect selected results in seconds, showing a local date near 2025.
• Input 1735689600000 with Auto detect selected results in milliseconds, converting to the same date as the row above.

What happens on invalid input, and how this differs from other time tools

If the field is left empty, contains non-numeric text, or converts to a date outside what the browser Date object can represent, the page shows an error message and hides the results panel instead of leaving a stale value on screen. Fixing the input and clicking Convert again redisplays all five fields: local time, UTC, ISO 8601, Unix seconds, and Unix milliseconds.

This tool only converts between a numeric timestamp and a readable date in both directions. It does not convert a time into a third city's timezone, add or subtract days, or calculate business days; use this site's date difference calculator or business days calculator for those tasks instead.

How to use

1. Enter a Unix timestamp.
2. Choose seconds, milliseconds, or automatic detection.
3. Convert to see local, UTC, and ISO formats.

Use cases

• Inspect API creation times while debugging.
• Turn database epoch values into dates.

Who is it for

• Developers inspecting API, database, and server log timestamps
• Support teams comparing local time with UTC
• Students learning Unix epoch and ISO 8601 formats

Real examples

Good to know

• A Unix timestamp represents an instant and does not contain a timezone; timezone only changes how that instant is displayed.
• A trailing Z in ISO 8601 means UTC. Browser-local output can differ because of locale and daylight-saving rules.
• Very large or negative values may fall outside browser date limits and should be checked against the source system.