Date & Timestamp Converter
Convert between Unix time, ISO 8601, spreadsheet serial numbers and human-readable dates in any timezone — one value at a time, or a whole column at once.
Used for input without an offset, and for local output.
Convert a value
Convert a column
Ready to automate?
Simple Data Foundry can cast and reshape columns as they load, so the dates arriving in your sheet, base or table are already in the format you want.
Frequently Asked Questions
What is a Google Sheets serial date?
Sheets and Excel store dates as the number of days since 30 December 1899, with the time of day as the fractional part. 46000.5 is midday on a specific date. Exports often carry these raw numbers, which is why a date column sometimes arrives as five-digit numbers.
Why does my timestamp come out a day off?
Almost always a timezone boundary. A UTC timestamp late in the day is the following day in Asia-Pacific zones and the same day in the Americas — so a date-only conversion moves depending on the zone you convert in. Pick the zone your reporting uses, not the zone your laptop is in.
How does it handle 03/04/2026?
It cannot know whether that is 3 April or March 4, so it tells you rather than guessing silently. Set "Interpret as" to day-first or month-first and the whole conversion, including bulk mode, follows that choice.
Seconds or milliseconds?
Detected by length. A 10-digit number is read as seconds, 13 digits as milliseconds, and anything under 7 digits as a spreadsheet serial. You can override the detection with the "Interpret as" selector.
Is my data safe?
Yes. All conversion happens in your browser — nothing is uploaded and no server sees your values.