Cells
8,388,600
Native Windows app · 100% offline
Open the workbooks that make Excel freeze.
An Excel sheet stops at 1,048,576 rows. We open one filled right to that ceiling — 8.4 million cells — in about 13 seconds, on an ordinary laptop. A real 131 MB accounting workbook opened in about 10. Nothing is ever uploaded.
Launching soon · $29 one-time
See how it works
Data never leaves your PC
Read-only — never edits your file
The wall
It opens. Eventually. Maybe.
A heavy export can hold Excel hostage for minutes before it stops responding — and the bigger it gets, the worse it scales. Cloud viewers can open big files, but they make you upload the data first. For a ledger full of customer names and account numbers, that's not an option.
Today
minutes
Waiting, then a white window
The spinner runs, the window greys out, and you're not sure whether to wait or kill it. The alternative is uploading financial records you're not allowed to send anywhere.
With FastSheet
~13s
A completely full sheet, opened locally
1,048,575 rows — the .xlsx format's own ceiling — read on your own machine. Column stats, filter, find. Read-only, offline, done. Measured, not marketing.
Why it matters
Your data never leaves this PC.
Finance, accounting and ops teams handle records they're forbidden to upload — customer details, account numbers, year-end figures. FastSheet reads the file on your machine and never sends it anywhere. No account to create, no server holding your data, nothing uploaded. The file stays exactly where it is.
One network call, ever — when you click Activate
1,048,575 rows
a sheet filled to the .xlsx ceiling
~13s
to open it — measured
100%
offline — never uploaded
.xlsx · .csv
Excel & CSV, read-only
The benchmark
Here's exactly what we measured.
Numbers on a landing page are worth nothing if you can't check them. So here's the file, the machine, the spread across runs, and the limits — including the ones that don't flatter us.
The file
- Name
- full-sheet.xlsx
- Size
- 44,585,759 bytes (42.5 MB)
- Rows
- 1,048,575 + 1 header
- Columns
- 8
- Cells
- 8,388,600
A sheet filled to the .xlsx format's own ceiling of 1,048,576 rows. You cannot make a bigger single sheet — that limit belongs to the format, not to Excel and not to us.
The machine
- CPU
- Intel Core Ultra 7 265H
- RAM
- 15.5 GB
- OS
- Windows 11 Pro (26200)
- Build
- rustc 1.96.0, release
- Date
- 15 July 2026
An ordinary laptop, not a workstation. Your machine will differ — a PC with 8 GB of RAM has not been tested with a file this size.
The runs
- Run 1
- 10.5 s
- Run 2
- 14.0 s
- Run 3
- 14.3 s
- Run 4
- 12.7 s
- Average
- 12.9 s
Four runs, all of them shown. We quote ~13s, the average — not 10.5s, the one that would look best.
What this benchmark does not prove
- Speed follows cell count, not megabytes. A 42.5 MB file packed with 8.4 million cells takes longer than a 131 MB workbook that's heavy with formatting. Don't read "MB" as a speed predictor — we don't.
- The data is synthetic. It's a realistic ledger shape, generated to be genuinely full — but real files are messier (merged cells, hidden sheets, mixed formats) and may open slower.
- This measures the engine, via a command-line harness. What you see on screen also includes drawing the table, so it can feel slower.
- One machine, one config. Not a fleet. Not an average across hardware.
Reproduce it yourself: the file generator, the exact command and the full write-up ship in our repo as FULL_SHEET_BENCHMARK.md. If your numbers differ, we want to hear about it.
How it works
Three steps. No setup.
Open the file
Drag in a CSV or XLSX — a full Excel sheet, or millions of rows of CSV. It loads on your machine in seconds.
Read & explore
Instant column stats (sum, average, min/max), Excel-style filters, find across the whole file, jump to any cell.
Export the view
Save just the filtered rows to a new CSV. Your original file is never touched — FastSheet is read-only by design.
Pricing
Buy it once. Keep it.
One-time license · no subscription
$29
one-time
Pay once. No subscription. Free updates within the version.
Launching soon
The engine is done and fast today
Windows 10 & 11 · secure checkout
Checkout opens shortly — we're finishing distribution. The app already runs; this page is honest about where we are.
Questions
Straight answers.
Is my data really private?
Your file data never leaves your PC — not a byte of it, ever. To be precise rather than glib: FastSheet makes exactly one network call in its entire life, to our licensing provider, at the moment you click Activate. It sends your licence key — never your file, never your data. After that it never phones home, and it never calls out on its own. Watch it with any firewall monitor; that's the whole story, and we'd rather you check than take our word.
How big a file can it open?
We open a completely full Excel sheet — 1,048,575 rows, 8.4 million cells, 42.5 MB — in about 13 seconds (measured). A real 131 MB accounting workbook, roughly 1.36 GB once unpacked, opened in about 10. One caveat worth knowing: speed tracks cell count, not file size — a smaller file packed with more cells can take longer than a bigger one. FastSheet reads the file into memory, so it's tuned for large files, not 50 GB datasets.
Will it change my file?
No. FastSheet is read-only. To keep a subset, it exports a brand-new file — your original is never modified.
When can I buy it?
Soon. The engine is finished and fast today; we're setting up checkout and signing. This page will switch to a buy button the moment it's live — no waitlist games.
Windows only?
Yes, Windows 10 and 11 for now. Mac is on the roadmap if there's demand.
Subscription?
No. One-time price, one-time payment. You keep the app.