Dummy PNG File Generator
Every dummy PNG file is a valid image at the width and height you pick, padded to the exact byte size.
Sample PNG files, ready to download:
One click, exact size (1 KB = 1,024 bytes), default options, built in your browser.
A dummy PNG file is a real PNG image made for testing, with a small badge showing its own file name and dimensions. Download one free at the exact size you need, from 100 Bytes to 50 MB. Set the width and height under Options (800 x 500 by default, up to 8,192 x 8,192) and you have a test image for uploads, thumbnails, size limits and validation rules. No digging through your photo library, and nothing personal in the file. Need a lossy photo format instead? Use a dummy JPG file.
How we check it: every generated file must be exactly the size you set and pass a decode in headless Microsoft Edge at the chosen width and height, plus our own PNG chunk and CRC checks; the last browser run on 21 October 2026 passed 520 of 520 cases (how the files are made and checked).
What is inside a dummy PNG file
It is an ordinary PNG with one extra chunk that brings it to the size you set (how we build and check these files):
- An RGB image without an alpha channel, at exactly the width and height you chose. The picture is a dark slate card with a faint grid, a soft blue glow and a centred badge that shows the file name and a line such as "800 × 500 • DummyFiles.com".
- The pixels are compressed by your browser's own PNG encoder, so the file looks like any PNG a web app exports.
- The extra bytes sit in a private ancillary chunk named dmMY, just before the IEND end marker, with a correct CRC-32. PNG readers skip ancillary chunks they do not recognise, so the image displays the same at 50 KB or 50 MB.
- The smallest possible file depends on the dimensions and on your browser (roughly 20 to 30 KB at the default size). Ask for less and the tool tells you the exact minimum instead of handing you a broken file.
What a dummy PNG file is used for
Image upload limits
Check that an avatar or attachment field accepts a PNG one byte under your limit and rejects one byte over it, with an error a person can read.
Thumbnails and resizing
Give your resizer a wide 3000 x 200 banner, a tiny 16 x 16 icon and a huge square, and see which one breaks the crop.
Dimension rules
Test rules like "at least 1080 pixels wide" or "square images only" with an image that is exactly on, above or below the line.
Storage and CDN tests
Push large, valid PNGs through object storage, image CDNs and caches to measure transfer time and cache behaviour.
Test an image upload limit with a dummy PNG
Make three files around the limit: one byte under, exactly at it, and one byte over. Set the unit to Bytes and type the counts, for example 2097151, 2097152 and 2097153 for a 2 MB limit. Keep the same width and height for all three, so the size is the only thing that changes.
Then check which megabyte your stack means. 2 MB is 2,097,152 bytes on this site, and PHP reads its default upload_max_filesize of 2M the same way. A form that says "max 2 MB" may still mean 2,000,000 bytes, and that 97 KB gap is exactly where upload bugs hide.
| Limit | Size | Notes |
|---|---|---|
| nginx client_max_body_size (default) | 1 MB 1,048,576 B | Requests with a larger body get HTTP 413. |
| PHP upload_max_filesize (default) | 2 MB 2,097,152 B | Also capped by post_max_size, so raise both. |
| AWS Lambda synchronous invocation payload | 6 MB 6,291,456 B | Applies to request and response. |
| Amazon API Gateway REST API payload | 10 MB 10,485,760 B | Hard quota for REST APIs. |
| Outlook default attachment limit (Exchange accounts) | 10 MB 10,485,760 B | Administrators can change it. |
| Outlook attachment limit (internet accounts) | 20 MB 20,971,520 B | Per Microsoft Outlook guidance. |
| Gmail message size limit | 25 MB 26,214,400 B | Attachments grow about a third when encoded, so a 20 MB file can already be too big. |
File size and pixel size are two different tests
Most image validators check two separate things: the size in bytes and the dimensions in pixels. In a real photo they move together. Here they do not. A 10 MB dummy PNG at 800 x 500 has the same pixels as a 30 KB one; the rest is padding. So you can test a byte limit without tripping a pixel limit, and the other way round.
When you want an image that is expensive to process, raise the dimensions instead. 8,192 x 8,192 is about 67 million pixels, enough to see whether your server decodes whole images into memory before resizing them. Desktop browsers handle that size; some phones refuse to draw a canvas that large and you get an error message instead.
PNG, JPG or WebP for your test?
Use PNG when the code path cares about lossless images or the image/png MIME type. Use a dummy JPG file for photo uploads, since phones and cameras save JPEG, and a dummy WebP file to check that a newer format gets through. Running all three takes a minute and catches the classic "we only allowed .jpg" bug.
PNG file details
- Extension
- PNG .png
- MIME type
- image/png
- Smallest size
- 100 Bytes
- Largest size
- 50 MB
- Contents
- Lossless PNG image (opaque RGB) at the width and height you choose (default 800 x 500); extra size is a private padding chunk before IEND
Dummy PNG file FAQ
Is the dummy PNG a real image?
Yes. It is a standard PNG that browsers decode at the width and height you chose. We check the generator in Microsoft Edge and with our own PNG checker, which verifies the signature, the chunk order and every CRC-32.
What is a PNG file and how do I open it?
PNG (Portable Network Graphics) is a lossless image format. Any web browser opens it, as do Photos on Windows, Preview on macOS and almost every image editor. Double-click the downloaded file or drag it into a browser tab.
Can I choose the width and height?
Yes. Open Options and set the width and height in pixels, from 1 to 8,192 each; the default is 800 x 500. The file stays exactly the size you set. If that size is too small for the dimensions, the tool tells you the minimum.
How is the exact file size reached?
The extra bytes go into a private PNG chunk placed before the end marker. Image viewers ignore that chunk, so the picture looks the same at any file size.
Is the PNG transparent?
No. It is an opaque RGB image with no alpha channel, so it will not exercise your transparency handling.
How large can a dummy PNG file be?
Up to 50 MB, with dimensions up to 8,192 x 8,192 pixels. Very large canvases can fail on phones, so make those on a desktop browser.
Is the image uploaded anywhere?
No. It is drawn and encoded in your browser and never sent to a server.