Unix Timestamp Converter

Translate a timestamp into UTC or turn an explicit UTC date and time into epoch seconds or milliseconds. Choose the direction and unit, enter a value, then select Convert. Units are never guessed from the number of digits.

Convert an explicit Unix timestamp to UTC or a UTC value to seconds or milliseconds. The unit is never guessed.

Conversion input

Result

Enter a value and select Convert.

Conversion stays in your browser; timestamps are not uploaded, saved or placed in the URL. Timestamps can reveal activity. Copy uses your clipboard only when requested.

Convert an explicit timestamp or UTC value

Choose Timestamp to UTC or UTC to Timestamp. Select Seconds or Milliseconds: this selects the timestamp input or the primary timestamp output. Each format keeps its own draft when you switch; switching never converts one draft into another.
Use digits 0–9 and a dot for fractional seconds, with at most three fractional digits. Milliseconds must be an integer. UTC input uses YYYY-MM-DDTHH:mm:ssZ, optionally with one to three fractional digits before Z. Use current time fills only the active draft from this device's clock and waits for Convert.
Read the primary answer, the other two representations and the visible model qualifications. Open the method to follow the active input through integer milliseconds. Copy result summary includes the current input, direction, unit and qualified outputs; clipboard denial offers the same selected text. Clear empties all drafts and restores the defaults.

Epoch units, UTC and the conversion model

The epoch reference is 1970-01-01T00:00:00Z. Seconds and milliseconds are different units: one second is 1000 milliseconds. A timestamp's digit count is not a reliable declaration of its unit. Check the API, database or file specification that supplied it.

UTC output always has three fractional digits and a final Z. Epoch seconds also have three fractional digits; milliseconds are an integer. These machine-readable values use ASCII digits, a minus sign when needed and a dot without grouping in every language. Accepted millisecond values are represented exactly; this does not certify the accuracy of a source clock.

The accepted date range is year 0001 through 9999, using Gregorian leap-year rules throughout. Before 1970, negative values follow this tool's proleptic-Gregorian extension, not a universal POSIX definition or historical UTC reconstruction. The model also does not predict future UTC policy or reconstruct local calendars.

Every model day has 86400 seconds. Leap-second labels such as 23:59:60 are deliberately rejected, and no leap-second table is applied. Timestamp differences across leap events must not be described as exact elapsed SI or TAI time. Offsets, local zones and daylight-saving rules are outside this converter.

Examples that reveal units and signs

Seconds 1234567890.123 and milliseconds 1234567890123 both give 2009-02-13T23:31:30.123Z. The seconds input 1.001 gives exactly 1001 milliseconds and 1970-01-01T00:00:01.001Z, without rounding away the last millisecond.

The value 1000000000 gives 2001-09-09T01:46:40.000Z when explicitly interpreted as seconds, but 1970-01-12T13:46:40.000Z when interpreted as milliseconds. The converter does not choose between them for you.

Milliseconds -1 is one millisecond before the epoch: 1969-12-31T23:59:59.999Z and -0.001 seconds, not -1.999 seconds. UTC input 2000-02-29T00:00:00Z is valid; the same February 29 in 1900 or 2100 is not.

Deliberate input and timekeeping limits

Seconds accept an optional ASCII sign, leading zeroes and up to three fractional digits after a dot. Milliseconds accept an optional sign and integer digits only. There is no exponent notation, decimal comma, grouping, bare decimal fraction, trailing dot or rounding of extra precision. Raw drafts longer than 64 UTF-16 code units are rejected before edge trimming.

UTC input requires four year digits, uppercase T and Z, seconds, valid calendar fields and at most three fractional digits. Year 0000, expanded years, missing zones, offsets including +00:00, hour 24, leap seconds and invalid dates are rejected rather than normalized. Local-time strings and microsecond or nanosecond precision are unsupported.

Use current time captures the browser's device clock once; it is not network-synchronized or independently verified by this tool. There is no running clock, automatic conversion, file export or saved history. Edits or profile changes remove the previous answer so that a stale conversion cannot look current.

Keep timestamps on this device

Conversion runs in the browser without uploading timestamps, saving drafts or putting values in the page URL. A timestamp can still reveal activity. Copy runs only when you request it, and copied data is then subject to the other applications and clipboard services you use.

Unix timestamp conversion questions

No. Select Seconds or Milliseconds using the source system's documentation. Digit count is only a convention in some data sets, not proof of a unit. A value outside the selected format's supported range is rejected rather than reinterpreted.

The minus sign applies to the whole decimal magnitude: one millisecond before zero is -0.001 seconds. Calendar decomposition uses a previous second plus a positive remainder, but that is not how a signed decimal seconds string is rendered. Negative dates also carry the tool's pre-1970 model qualification.

No. Use the explicit uppercase UTC format with T, seconds and a final Z. Offsets, even +00:00, local times and daylight-saving conversion are outside this tool's strict input subset. Changing the page language does not change the timezone or the machine-readable values.

No universal historical-time claim is made. POSIX leaves the negative/pre-1970 relationship undefined. This converter deliberately extends its UTC-based model with the proleptic Gregorian calendar through year 0001; it does not reconstruct historical UTC, local calendars or future timekeeping policy.

No. The model uses 86400 seconds per day, rejects second 60 and applies no leap-second table. Resolution is one millisecond: seconds may have up to three fractional digits, and extra precision is rejected, not rounded. This is representation precision, not a guarantee about clock accuracy.

Seconds, milliseconds and UTC have independent drafts. Changing direction or unit preserves those drafts but removes the old result until Convert succeeds again. Copy result summary always uses the current qualified snapshot and language; if clipboard access fails, the identical text is offered for manual copying. Clear resets every draft and the default profile.