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Merge two spreadsheets or join two CSV files

Drop two CSV or Excel files, say which column they share, and download one merged file. No VLOOKUP or formulas, and files too big for Excel are fine.

Drag & drop 2 spreadsheets here, or click to browse

Up to 350MB per merge

No description? Just click Combine — we auto-detect the join key. Free to try, no sign-up.

Join two files without VLOOKUP

Too Big for Excel? No Problem.

Stop dealing with frozen screens when working with massive exports. TenMil handles huge files right in your browser — no plugins, no waiting, no crashing.

Ditch the Syntax.

Stop Googling INDEX/MATCH or debugging #N/A errors. Just describe what you want, and our AI intelligently maps your column headers so you get a flawless merge without writing a single formula.

Built for Operators.

Perfect for enriching data sets like marketing outreach lists, mapping e-commerce customer data, combining Shopify sales exports, or matching payment logs.

Merging two files: VLOOKUP vs TenMil

CapabilityExcel VLOOKUPTenMil.ai
Logic TypeManual Formula (Cell-based)Natural Language (Intent-based)
Data ScopeOne-directional lookup onlyLEFT, INNER & FULL OUTER joins
Setup TimeWrite & debug formulasAuto-detected join key
AccuracyManual & error-proneDeterministic engine — same result every run
StabilityFormulas break on column moveAI-suggested keys & join type
Unmatched Rows#N/A errors scattered in cellsHighlighted & counted per bucket
Input SourcesLocal files onlyLocal files
ExportManual copy-pasteExcel or CSV (one click)
ProcessingLocal (single-threaded)In-browser SQL engine, no upload required

What happens to your files during a merge

Zero-Data-Retention Security

Processed securely. Never stored on our servers.

To map your files correctly, we send a small sample of your data — column names and a limited number of example values — to our AI service over an encrypted connection. Your full dataset is processed locally: never uploaded, never stored on a server, and wiped the moment you close the tab.

100% Deterministic Math

Zero hallucinations, every time.

Standard AI struggles with exact math and data privacy. TenMil solves this by separating the intelligence from the execution. Our schema-aware AI parses your plain-English commands and generates the underlying data logic, completely insulated from your raw files. Our local SQL engine then executes that logic with reliable, repeatable results.

Learn how it works

How to Merge Two Large Spreadsheets by a Shared Column (No VLOOKUP, No Formulas)

Merge two large spreadsheets by a shared column in minutes using AI. Upload both files, review the match plan, refine the list in plain English, then export to Excel.

Phrasebook

Plain-English phrases that work in TenMil's chat, with exact results.

Video: How to combine two large spreadsheets with AI by matching on a column.

Watch a full two-file merge, start to finish.

All resources →

Frequently Asked Questions

How do I merge two spreadsheets by a shared column?
Drop both files on this page and say how they match, for example "match on email" or "join on product ID". TenMil finds the column both files share, shows how many rows will match before it runs, and then merges them in your browser. Download the result as CSV or Excel.
How do I join two CSV files?
The same way. Drop both CSV files and type which column links them, for example "join on order ID". You can also join a CSV to an Excel (.xlsx) file, or two Excel files.
What if the shared column has a different name in each file?
That works. Say something like "match Email in the first file to Contact email in the second". Values that differ only by capitalization or extra spaces still match.
Which kinds of join can I do?
Keep every row from the first file and add matches from the second (a left join), keep only rows found in both files (an inner join), or keep everything from both (a full outer join). If the two files have the same columns, you can stack them into one list instead.
What happens to rows that don't match?
They are counted, not hidden. The result shows how many rows matched and how many did not, and an Excel download puts the unmatched rows on their own sheet so you can check them.
What if a value appears more than once in the join column?
Repeated values can multiply rows in a merge. TenMil checks for this before it runs and asks how to handle the repeats, for example by keeping only the first match.
How big can the two files be?
Up to 350 MB combined, well past Excel's 1,048,576-row limit. An Excel file counts as 3 times its size toward that cap. The join runs in your browser with DuckDB, so your files are not uploaded. Only column names and a few sample values are sent to plan the merge.
Is merging free?
Yes. Merging and previewing the result are free, and free use includes 3 downloads a day. Pro removes the daily download limit for $15 a month or $150 a year.

Looking for specifics? See all TenMil facts →