What Excel is
An Excel workbook is a zip archive of XML parts describing sheets, cells, formulas, styles and charts. The .xlsx extension is that format; .xls is the older binary one from before 2007.
Finance, operations and anyone who received a file from finance or operations.
What CSV is
CSV is a text file where each line is a row and commas separate the fields. There is no type system, no formatting and no second sheet. Every value is text until something downstream decides otherwise.
Almost every database, analytics tool and spreadsheet can read and write it, which is why exports default to it.
What changes when you convert Excel to CSV
Only the first sheet is read, and cells are read as the text Excel displays rather than the number underneath. That matters for dates: a cell showing 15/03/2026 arrives as that string, not as a serial number you would then have to decode.
Any value containing the delimiter, a quote or a line break gets wrapped in quotes, and embedded quotes are doubled. That is the rule in RFC 4180 and it is what spreadsheet software expects.
Formulas are gone, and their results stay. A cell holding =SUM(B2:B40) becomes the number it evaluated to. There is no way to keep the formula, because a CSV has no concept of one.
Formatting is gone too. Bold, colours, borders, conditional formatting, merged cells, frozen panes and column widths are all properties of the workbook, not of the data. What survives is the values.
Only the first sheet is converted. A workbook with twelve monthly tabs produces one CSV of January, not twelve files. Copy the sheet you want into its own workbook, or paste its cells straight into the box above.
Cells are read as the text Excel displays. A date cell showing 15/03/2026 arrives as that string rather than as the serial number 46096, which is what you get from most command line converters and then have to decode.
What carries over from Excel to CSV
Excel records 3 things about a table that CSV has no way to hold.
Excel distinguishes a number from the text of a number; CSV does not, so every value arrives as text and has to be re-parsed by whatever reads it next.
An empty cell and a missing one are the same thing in CSV, so a null and an empty string in the Excel both come out blank and can no longer be told apart.
Anything visual in the Excel - weight, alignment, colour, column widths - has no counterpart in CSV and is dropped. The values are what survives.
The result can be read a record at a time, and appended to by adding to the end of it. That is worth having for a table too large to hold in memory, and it means a CSV file that is cut off part way through still gives you every record before the cut.