Unix Timestamp Converter
Convert Unix seconds or milliseconds to an explicit UTC date/time, or convert a UTC Gregorian date/time to both timestamp forms.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Count milliseconds relative to 1970-01-01 00:00:00 UTC. Keep the UTC interpretation explicit and validate the complete calendar date before converting.
Unix milliseconds=1000×Unix seconds; epoch=1970-01-01T00:00:00Z
Worked example
Unix 0 is 1970-01-01T00:00:00.000Z. Unix −0.001 seconds is 1969-12-31T23:59:59.999Z.
Assumptions and input details
Supports Gregorian years 0001–9999 and millisecond precision. Timestamp seconds accept up to three fractional digits; milliseconds are whole integers. No scientific notation or digit separators. Date input requires a four-digit year and seconds, with optional 1–3 millisecond digits and optional Z. It always means UTC, never browser local time. Invalid dates and leap-second labels such as 23:59:60 are rejected; Unix/JavaScript time does not represent leap seconds as additional distinct seconds. No guessing whether a large number means seconds or milliseconds.
References: ECMAScript time values
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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