Free tool · ICO and PNG · Runs in your browser
Convert PNG to ICO
Short answer
Choose a PNG, JPG or other picture and the tool writes an ICO file with 16, 32 and 48 pixel icons in it, in your browser with no upload. The files in our tests were 4.2 KB to 11 KB, and every one was read back correctly by ffprobe and by the browser. A square picture of at least 48 pixels works best.
Nothing is uploaded: the icons are made in your browser. Simple, bold shapes stay readable at 16 px.
Key takeaways
- One ICO holds three sizes: 16 px, 32 px, 48 px. Each is stored as a PNG inside the ICO, which Windows Vista and later read.
- The files are small: the ICO was 4.2 KB to 11 KB for four very different pictures, and the 512 pixel PNG 234 KB to 630 KB.
- It checks out: ffprobe, an independent parser, found three PNG frames of 16, 32 and 48 pixels in every file, and the browser opened every one.
- Small sizes are a test of your picture: the 16 pixel icon of our insignia matched a Lanczos reduction at SSIM 0.88, the photograph at 0.97. Bold shapes with few details survive; a wide document does not.
- Google Search Central says a favicon must be square and at least 8 × 8 px, and recommends one larger than 48 × 48 px; it accepts ICO and PNG, among other formats.
Measured: what the tool makes
Measured in headless Chromium with the tool's own code. Four pictures (a 5380 × 5432 mission insignia PNG with transparency, a 3840 × 3877 photograph, a 2122 × 2644 portrait and a 3827 × 1588 document scan, all public domain NASA and archive files) were turned into the icons with each of the two square options. The ICO was then read back by ffprobe, an independent parser, and opened by the browser. SSIM compares each icon with a Lanczos reduction of the same square made by ffmpeg (1.0 would be identical).
| Picture | favicon.ico (3 sizes) | 180 px PNG | 192 px PNG | 512 px PNG | Time |
|---|---|---|---|---|---|
| Mission insignia (PNG with transparency, 5380 × 5432) | 10.0 KB | 58 KB | 65 KB | 345 KB | 4.1 s |
| Photograph (JPG, 3840 × 3877) | 9.2 KB | 75 KB | 85 KB | 630 KB | 1.9 s |
| Portrait (JPG, 2122 × 2644) | 11 KB | 80 KB | 90 KB | 553 KB | 0.6 s |
| Wide document scan (JPG, 3827 × 1588) | 7.9 KB | 69 KB | 76 KB | 561 KB | 0.5 s |
Making all the icons took 0.5 to 4.1 seconds on a desktop browser, most of it reading the large picture.
Measured: how clean the small sizes are
| Picture | 16 px | 32 px | 48 px | 180 px | 512 px |
|---|---|---|---|---|---|
| Mission insignia (PNG with transparency, 5380 × 5432) | 0.88 | 0.94 | 0.93 | 0.97 | 0.96 |
| Photograph (JPG, 3840 × 3877) | 0.97 | 0.95 | 0.95 | 0.97 | 0.98 |
| Portrait (JPG, 2122 × 2644) | 0.99 | 0.96 | 0.98 | 0.99 | 0.98 |
| Wide document scan (JPG, 3827 × 1588) | 0.91 | 0.85 | 0.85 | 0.94 | 0.98 |
The browser reduces the picture in steps of at most half, which keeps the icons clean; the score is lower at 16 pixels because tiny details become a few pixels and small differences between reducers count for more. It says how stable the reduction is, not whether your logo is readable at 16 pixels: look at the preview.
Crop or fit inside a square?
A favicon is square, so a wide or tall picture must be cropped or padded. We measured both on the wide document scan: cropped, the ICO was 7.9 KB and the 32 pixel icon scored 0.85; fitted inside with transparent padding, the picture shrinks to a thin strip in the middle, the ICO was 4.2 KB and the 32 pixel icon scored 0.40.
| Picture | Option | ICO size | 32 px SSIM |
|---|---|---|---|
| Mission insignia (PNG with transparency, 5380 × 5432) | Crop to a square | 10.0 KB | 0.94 |
| Mission insignia (PNG with transparency, 5380 × 5432) | Fit inside a square | 10.0 KB | 0.92 |
| Photograph (JPG, 3840 × 3877) | Crop to a square | 9.2 KB | 0.95 |
| Photograph (JPG, 3840 × 3877) | Fit inside a square | 9.2 KB | 0.95 |
| Portrait (JPG, 2122 × 2644) | Crop to a square | 11 KB | 0.96 |
| Portrait (JPG, 2122 × 2644) | Fit inside a square | 9.5 KB | 0.93 |
| Wide document scan (JPG, 3827 × 1588) | Crop to a square | 7.9 KB | 0.85 |
| Wide document scan (JPG, 3827 × 1588) | Fit inside a square | 4.2 KB | 0.40 |
For a logo that is already square, the two options give nearly the same icons. For a wide logo, a square mark or monogram made for the purpose will always read better at 16 pixels than a shrunken wide logo.
What goes in an ICO file
An ICO file starts with a directory that lists every image in it, followed by the images. Each image can be stored as a bitmap or as a complete PNG. Wikipedia notes that Windows Vista added 256 × 256 icons and PNG compression, and that Microsoft recommends storing 256 × 256 images as PNG; here every frame is a PNG, which keeps the file small. In the directory a size of 256 is written as 0.
| Bytes | Field | Value written by this tool |
|---|---|---|
| 0 to 1 | Reserved | 0 |
| 2 to 3 | Type | 1 (icon) |
| 4 to 5 | Number of images | 3 |
| Per image, 16 bytes | Width, height, colors, planes, bit depth, size, offset | Size of each icon, 1 plane, 32 bits, offset into the file |
What to put in the page
- Upload favicon.ico to the root of your site and add the two lines of HTML shown under the tool.
- Google Search supports one favicon per site, defined by the hostname, and needs Googlebot to be able to crawl both the home page and the favicon file.
- Keep the favicon URL stable: Google asks that it is not changed often.
- Use the 192 and 512 pixel PNGs where an app manifest asks for icons, and the 180 pixel PNG as the Apple touch icon.
Free tools:Favicon generator with PNG sizesRemove the background from a logoConvert any image to PNG
How the files were checked
Every ICO written in the measurements was opened by ffprobe, which reported three PNG streams of 16, 32 and 48 pixels, and by the browser as an image. The ZIP the tool offers is written with the files stored uncompressed, since PNG and ICO are already compressed.
Questions people ask
How do I make a favicon.ico?
Choose your logo above. The tool writes favicon.ico with 16, 32 and 48 pixel icons, plus PNGs of 180, 192 and 512 pixels, and a ZIP of all of them.
What size should a favicon be?
Google Search Central says a favicon must be square and at least 8 × 8 pixels, and recommends one larger than 48 × 48 pixels. The ICO here has 16, 32 and 48 pixel frames; the PNGs go up to 512.
How do I convert a PNG to ICO?
Choose the PNG above and download favicon.ico. The conversion happens in your browser.
Can I keep a transparent background?
Yes. A PNG with transparency keeps it in the icons. With the "fit inside a square" option, the padding is transparent too.
Does it work on a wide logo?
It can crop to the middle or fit the whole logo inside a square, but a wide logo is hard to read at 16 pixels. A square mark works better.
Is my picture uploaded?
No. The icons are made in your browser.
Why three sizes in one ICO?
An operating system or browser picks the frame that fits where the icon is shown, so a tab can use 16 pixels and a taskbar or bookmarks list a larger one.
Where do I put the file?
In the root of your site as /favicon.ico, with the link tags shown under the tool in your page head.
Related
Sources and how we checked
- Google Search Central: Define a favicon to show in search results (read 2026-10-09)
- Wikipedia: ICO (file format) (read 2026-10-09)
- FFmpeg Documentation: ffprobe (used to read the ICO back) (read 2026-10-09)
Reviewed October 9, 2026. The measurements ran the tool's own code in headless Chromium and read the ICO files back with ffprobe. The script and the results are in data/seo/hub/evidence/2026-10-09/favicon.