20 MB BMP sample

A BMP file of exactly 20,971,520 bytes. It is a valid Windows bitmap file, generated by this site. Compare its checksum and test it with the parser used by your application. Use it wherever you need a 20 MB sample, test or dummy BMP file.

sample-bmp-20mb.bmp

20 MB20,971,520 bytes

Download 20 MB BMP

Created in your browser in a few seconds, then checked against the SHA-256 checksum. No sign-up.

Type: image/bmp
SHA-256: 0b95b64840d1e694d4ca3a7972ad8cd6bd003e933e7cc5a4c751e1cb36e5d3e7
Delivery: Created in your browser from static generator assets (how it works).

What is in this file

An uncompressed 3053 × 2289 test card. 4,226 bytes of unused space between the header and the pixel array bring the file to the exact size.

Dimensions	3,053 × 2,289 px
Bit depth	24-bit RGB
Compression	None (BI_RGB)
Header	BITMAPINFOHEADER (40 bytes)
Row order	Bottom-up

First bytes of the file

The first 64 bytes of sample-bmp-20mb.bmp as a hex dump: offset, bytes, then the same bytes as text. The BMP signature is 42 4D.

00000000  42 4d 00 00 40 01 00 00  00 00 b8 10 00 00 28 00 |BM..@.........(.|
00000010  00 00 ed 0b 00 00 f1 08  00 00 01 00 18 00 00 00 |................|
00000020  00 00 48 ef 3f 01 13 0b  00 00 13 0b 00 00 00 00 |..H.?...........|
00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 |................|

Preview

Creates the file in your browser and shows it here. Nothing large is downloaded from our server.

Where 20 MB matters

A 20,971,520-byte file: right at the default attachment limit of Outlook, and just under the 25 MB ceilings of Gmail and GitHub web uploads. These are the default limits a file of this size is useful for testing:

System	Limit	Note
Microsoft Outlook	20 MB of attachments by default for internet mail accounts	This file is right at the limit; add a second attachment and it is exceeded.
Gmail	25 MB per message	Under the limit, although email encoding adds about a third in transit.
GitHub web uploads	25 MiB per file added through the browser	Accepted. Pushing with Git allows larger files.
Cloudflare Pages assets	25 MiB per file	The largest round size that can be served as a static asset.
Amazon API Gateway	10 MB payload	Rejected; the upload has to go directly to object storage.
ASP.NET Core (Kestrel)	About 28.6 MB request body by default	Accepted with room for the multipart overhead.

All 20 MB sample files

Use this file for

Testing image resizing and memory use
Checking that services convert BMP to a web format
Testing decoders for legacy formats

Testing notes for BMP

Row padding and bottom-up order are the usual causes of skewed or upside-down images in hand-written decoders.
Some validators accept BMP by MIME type but have no decoder for it, which fails later in the pipeline.

BMP format reference

Technical details

File name	sample-bmp-20mb.bmp
Format	BMP (Windows bitmap)
Extension	.bmp
MIME type	image/bmp
Size	20,971,520 bytes (20 MB)
Kind	Binary
Signature	42 4D
SHA-256	0b95b64840d1e694d4ca3a7972ad8cd6bd003e933e7cc5a4c751e1cb36e5d3e7
Created	2026-10-23
Validation	See the listed size and SHA-256. Small downloads are checked in the browser; verify streamed downloads manually. A hash match does not prove parser compatibility.
Preview	Available on this page
Source	Generated in your browser by this site's generator; not copied from elsewhere
Licence	Free to use, modify and redistribute (terms)
Category	Images

Check the stated structure and checksum against your application requirements. As with any download, scan the file with your own security tools before opening it. How files are made and checked

Verify your copy

This file is created in your browser, so it has no direct URL for curl or wget. The generator is designed to produce reproducible bytes. After saving, compare the checksum with the SHA-256 value above.

sha256sum sample-bmp-20mb.bmp     # Linux
shasum -a 256 sample-bmp-20mb.bmp # macOS

On Windows, run Get-FileHash sample-bmp-20mb.bmp -Algorithm SHA256 in PowerShell. For scripts and pipelines, save the file once and keep your own copy.

Related files

Questions about this file

Is this file exactly 20 MB?: Yes. It is 20,971,520 bytes, which is 20 MB in the binary units that operating systems and server limits use (1 KB = 1,024 bytes).
What is inside the 20 MB BMP file?: An uncompressed 3053 × 2289 test card. 4,226 bytes of unused space between the header and the pixel array bring the file to the exact size.
What bit depth are the BMP samples?: 24-bit RGB with no compression and no colour table.

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