CSV ↔ XLSX Converter

How direction is chosen

The tool looks at the file you drop: a .csv file converts to .xlsx, while a .xlsx or .xls file converts to .csv. There's no separate mode switch to get wrong.

Multiple sheets

CSV is a single-sheet format, so converting to .xlsx always produces a workbook with one sheet. Converting a multi-sheet .xlsx or .xls file only exports one sheet at a time — use the sheet selector that appears for multi-sheet files to choose which one, and download each separately if you need more than one as CSV.

How data is handled

CSV to XLSX: by default every value is kept exactly as typed, so 02134 and 007 keep their leading zeros, "1,5" stays the text 1,5, and 1e3 and 2024-01-05 stay as written. Tick "Detect numbers and dates" to have number-, true/false- and date-like text converted the way a spreadsheet would (02134 becomes 2134, "1,5" becomes 15, 1e3 becomes 1000). Comma, semicolon and tab separators are detected automatically either way.

XLSX to CSV: numbers are written as stored, so a cell showing 1,234.50 is exported as 1234.5. Tick "Use displayed formatting" to export what the sheet shows instead, written in quotes because it contains a comma. Dates are written in the sheet's date format either way, and the stored value of 0.1 + 0.2 is exported in full as 0.30000000000000004.

What doesn't carry over

CSV is plain text, so converting an .xlsx to .csv keeps the cell values but drops formulas (only their last calculated result is kept as text), formatting, colors, charts, and multiple sheets. Going the other way, converting .csv to .xlsx, produces a plain workbook with no formatting applied.

What the preview and download show

The preview table shows the first 6 rows with blank rows hidden, but the download contains the whole file. A CSV becomes a workbook with one sheet named Sheet1, saved under your file name with .xlsx on the end. A spreadsheet becomes a CSV with .csv on the end. Files can be up to 20 MB, and anything that does not end in .csv, .xlsx or .xls shows "Please choose a .csv, .xlsx, or .xls file."

Awkward CSV files

• Rows of different lengths are kept as they are. If one row has more fields than the header, the sheet is made as wide as the widest row, and shorter rows have empty cells.
• A quoted field with a line break in it stays in a single cell. Blank lines in the CSV become empty rows in the workbook, although the preview hides them.
• A semicolon file is detected only when commas do not get in the way. If it has unquoted decimal commas, such as 1,5;2,5, the commas win and the columns come out wrong. Put quotes around those values, or save the file with commas or tabs.
• A single cell can hold 32,767 characters at most. A longer value makes the conversion stop with "Couldn't parse that CSV file."

What "detect numbers and dates" changes

Off, every value stays text. On, 50% becomes 0.5, (5) becomes -5, and TRUE and FALSE become true and false, along with the number and date conversions described above. Turn it on for data you want to add up, and leave it off for postcodes, phone numbers, IDs and anything with leading zeros.