Formats/XLSX vs CSV
XLSX vs CSV: Which Spreadsheet Format Should You Use?
XLSX and CSV are the two formats you meet most often when working with data in rows and columns, and people frequently treat them as interchangeable — until a CSV mangles a phone number or an XLSX will not import into some system. They are good at genuinely different things. The short version: XLSX is a full, living spreadsheet, while CSV is a plain, universal list of raw values. Knowing which you actually need saves a lot of frustration.
What each format actually is
An XLSX file is a complete Excel-style workbook: it can hold multiple sheets, live formulas that recalculate, cell formatting, number and date types, charts, colours and conditional rules — all bundled in one document (technically a ZIP archive of XML). It is designed to be worked in, keeping a spreadsheet fully functional.
A CSV file is the opposite of rich: it is plain text, one row per line, with commas separating the columns and nothing else — no formulas, no formatting, no types, no multiple sheets. It is the lowest common denominator that virtually every program on earth can read and write, which is exactly why it is the universal format for importing and exporting raw data between systems that otherwise share nothing.
The trade-offs
XLSX keeps everything but is a richer, program-specific format — some systems, scripts and databases would rather not deal with its complexity, and it is overkill when all you need to move is a flat table. CSV keeps nothing but the values, which makes it wonderfully portable and easy for any tool to parse, but means it throws away formulas, formatting and anything beyond a single grid of text.
There is also the matter of size and speed: a CSV of a large dataset is compact and fast for programs to read, which is why data pipelines and analytics tools love it. An XLSX carries more overhead but earns it by keeping the spreadsheet alive and human-friendly.
The CSV pitfalls to watch for
Because CSV stores no type information, spreadsheet programs guess when they open one — and sometimes guess wrong. A ZIP code like `01234` can lose its leading zero and become `1234`; a long ID or credit-card-style number can be mangled into scientific notation; dates can be misread in a different regional order. Not every "CSV" even uses commas — in regions where the comma is a decimal separator, files often use semicolons — and there is no universal rule for character encoding, so a CSV that opens perfectly in one program can look garbled in another.
Most of this is avoidable: save as UTF-8, be deliberate about the separator, and when importing, tell the spreadsheet to treat sensitive columns as text rather than double-clicking and letting it guess. XLSX sidesteps all of these problems because it stores types and formatting explicitly — a number stays a number, a date stays a date.
How to convert between them
A common and sensible workflow is to keep your working file as XLSX — with its formulas and formatting intact — and export a CSV only when another system needs the raw data. OfficePad's spreadsheet editor opens both XLSX and CSV in the browser, lets you edit, and exports back to either, all on your device with nothing uploaded. When you export to CSV, remember you are deliberately flattening the workbook to plain values; when you import a CSV into XLSX, you are giving that flat data a home where formulas and formatting can be added.
Frequently asked questions
Should I save as XLSX or CSV?
Use XLSX when you need formulas, formatting, multiple sheets or charts — anything you will keep working in. Use CSV when you only need to hand a flat table of raw data to another program that will import it.
Why did my CSV change a ZIP code or long number?
CSV stores no type information, so the spreadsheet guessed — dropping a leading zero or converting a long number to scientific notation. Importing the column as text, rather than double-clicking the file, prevents it.
Does converting XLSX to CSV lose anything?
Yes, by design. CSV keeps only the raw values of a single sheet — formulas, formatting, multiple sheets and charts are all stripped away, leaving just the data.
Work with XLSX vs CSV on OfficePad
See also in the glossary: Character encoding, UTF-8, Metadata.