How to convert between CSV and Excel

Convert without opening Excel — which also avoids the changes Excel makes to your data on the way in.

CSV is plain text; .xlsx is a spreadsheet with types, formatting and multiple sheets. Converting directly avoids a set of well-known problems that arise when Excel opens a CSV.

Step-by-step

1. Add your file, CSV or .xlsx.
2. Convert.
3. Download.

The damage Excel does to CSVs

• Leading zeros are stripped. Postcodes and account numbers become numbers, and the zeros go.
• Things that look like dates become dates. This is the notorious one: gene names and part numbers silently converted, and the change is irreversible once saved.
• Long numbers become scientific notation, losing digits from identifiers.
• Accented characters break when the encoding is guessed wrongly.

These happen on opening, so a round trip through Excel can corrupt a file even if you change nothing and save it back.

Encoding

UTF-8 is used throughout, which is what keeps accented characters and non-Latin scripts intact. Most CSV corruption of the "é" variety is a file written in one encoding and read as another.

When you actually want Excel

Use .xlsx when formulas, formatting or several sheets matter. Use CSV when the data is the point and you want it readable by anything. CSV holds no formulas — converting a spreadsheet to CSV keeps the computed values and discards how they were computed.

Frequently asked questions

Will my leading zeros survive?

Converting directly preserves them. Opening a CSV in Excel is what strips them, which is a good reason to convert without going through Excel at all.

Do formulas convert?

Going from .xlsx to CSV keeps the results, not the formulas — CSV has no way to store them. Going the other way produces values rather than formulas.

Which encoding is used?

UTF-8, which keeps accented and non-Latin characters intact.