How to combine CSV files

Stack or join? Decide first

Combining CSVs usually means one of two things. Stacking appends rows: twelve monthly export files with the same columns become one yearly file. Joining merges columns: a customers CSV and an orders CSV become one file matched on customer ID. The methods below handle both, but the right choice depends on your files. See join vs. stack if you're unsure.

Method 1: Copy and paste (quick one-offs)

Open each CSV in Excel or Google Sheets, copy the data rows from each (skipping repeated header rows), and paste them under each other in a master sheet. Fine for two or three small files. Risky beyond that: it's easy to paste under the wrong column, and repeated headers sneak in as data rows.

Method 2: Power Query "From Folder" (repeatable stacks)

Put all CSVs in one folder, then in Excel go to Data → Get Data → From File → From Folder. Power Query combines every file, promotes the first row to headers, and lets you filter or transform before loading. This is the best native option for recurring monthly exports. It only stacks, though — for joins you need a separate merge step, and the interface takes practice.

Method 3: MergeStudio (no formulas, in your browser)

MergeStudio combines CSVs (and Excel files) without formulas or installs. Everything runs locally in your browser, so the files never leave your device.

1. Open the free merge tool.
2. Add your CSV files — select several at once.
3. Choose the sources to include.
4. Pick Stack Rows to append the files, or a join mode to combine them on a shared column such as an ID or email.
5. For a join, select the matching column separately for each file.
6. Preview the result, choose your output columns, and download one merged file.

For a column-matched walkthrough, see how to merge CSV files by a matching column.

Method 4: Command line (developers)

If the CSVs have identical headers, a one-liner works: on macOS/Linux, head -1 jan.csv > all.csv && tail -n +2 -q *.csv >> all.csv stacks files while keeping one header row. Fast and scriptable, but it assumes clean, uniform files and offers no join logic or preview.

Avoid the classic CSV pitfalls

• Repeated header rows. When stacking, keep the header from the first file only.
• Encoding issues. Files saved in different encodings (UTF-8 vs. Latin-1) can garble special characters — open the result and spot-check names.
• Delimiter mismatches. Some exports use semicolons instead of commas; make sure every file parses into the same columns.
• Numbers stored as text. IDs like 00123 can lose leading zeros when opened in Excel — a join on a mangled key silently misses rows.
• Trailing blank rows. Export tools often add empty rows that become junk records; filter them out before or after combining.

Frequently asked questions

How do I combine multiple CSV files into one Excel file?

Stack or join the CSVs with any method above, then save or download the result as XLSX. MergeStudio downloads the merged result directly as an Excel workbook.

Can I combine CSV files with different columns?

For stacking, align the columns first or the data will land in the wrong places. For joining, different columns are fine — you only need one shared matching column.

How do I merge CSV files by ID?

Use a join on the ID column: each row in the second file is attached to the row with the same ID in the first. In MergeStudio, select the ID column separately for each source.

Will combining CSVs keep my data private?

Only if the tool processes files locally. MergeStudio runs entirely in your browser — nothing is uploaded to a server.

What if my CSV files are too large to open in Excel?

Excel caps at about a million rows. A browser tool that streams the files can handle larger inputs than a spreadsheet grid comfortably displays — combine first, then filter down.