Convert CSV to Excel (XLSX)

1. 1Choose the CSV file. The delimiter is detected automatically.
2. 2Leave “Detect numbers and true/false” ticked to get numbers you can calculate with, or untick it to keep every value as text.
3. 3Click Convert to Excel and download the .xlsx file.

Values that Excel would alter stay text; plain numbers become numbers.

id,zip,phone,amount,gene
1,02134,0612345678,24.90,MARCH1
2,02139,0698765432,1200,SEPT2

id | zip   | phone      | amount | gene
 1 | 02134 | 0612345678 |   24.9 | MARCH1
 2 | 02139 | 0698765432 |   1200 | SEPT2

01Opening a CSV without Excel changing it

Double-click a CSV and Excel guesses the type of every value: it drops leading zeros (02134 becomes 2134), rounds numbers longer than 15 digits, and turns values such as 1-2 or MARCH1 into dates. In 2020 the HUGO Gene Nomenclature Committee renamed 27 human genes, including SEPT1 and MARCH1, partly because Excel kept converting their names into dates.

02Fixing broken accents

Excel reads a UTF-8 CSV that has no byte order mark with a legacy encoding, so é turns into é. An .xlsx file has no encoding to guess.

03Sending data to people who use Excel

A workbook opens with a double-click, with columns already sized to their content.

• Plain numbers such as 42, -3.5 or 1200 become Excel numbers.
• Numbers with a leading zero (02134), more than 15 significant digits, an exponent (1e5), a thousands separator or a decimal comma (1,5) stay text, because converting them would change them.
• true and false, in any case, become Excel booleans.
• Dates stay text exactly as written: 03/04/2024 is a different day in the US and in Europe, and guessing wrong would silently corrupt the data.
• The header row is always text.

The data goes into one sheet named after the file. Each column is sized to fit its content, up to 50 characters wide, and empty CSV cells stay empty in Excel.