What Is an ICO File?
ICO is the icon format Windows has used since its earliest versions, and it’s the format behind the classic favicon.ico that browsers show in tabs and bookmarks. An ordinary image file holds one picture. An ICO works as a container that holds several copies of the same icon at different sizes, and whatever displays it picks the size that fits.
That’s why converting a PNG to ICO involves more than changing the extension. A 512-pixel logo shrunk on the fly to 16 pixels in a browser tab can look muddy. An ICO carries a version that was already scaled down to 16 pixels, next to larger versions for places where the icon is shown bigger.
Which Sizes Are Inside the ICO
Every file this converter produces contains four sizes:
| Size | Where it’s typically used |
|---|---|
| 16×16 | Browser tabs, bookmarks, title bars, Explorer’s small-icon and details views |
| 32×32 | The same small spots on high-density (2×) screens |
| 48×48 | Windows desktop icons at the default “Medium icons” setting and 100% scaling |
| 256×256 | Large and Extra large icon views in File Explorer, and high-DPI displays |
256×256 is the largest size an ICO image can have. Windows scales it down for sizes in between, so a file with these four sizes looks sharp in every common view.
Each size is stored as a PNG inside the ICO, a layout Windows has supported since Windows Vista and every current browser reads. Storing PNGs keeps the file small and keeps transparency exactly as it was in your source image.
How to Use Your ICO File
As a website favicon. Rename the file to favicon.ico and put it in your site’s root folder. Browsers request /favicon.ico automatically when a page doesn’t declare an icon. To be explicit, add this to your page’s <head>:
<link rel="icon" href="/favicon.ico">As a Windows folder icon. Right-click the folder, choose Properties, open the Customize tab, click Change Icon…, then Browse to your .ico file. Keep the ICO in a permanent location. Windows stores the file’s path, not a copy of the icon, so if you move or delete the ICO the folder goes back to the default icon.
As a shortcut icon. Right-click the shortcut, choose Properties, and on the Shortcut tab click Change Icon…, then browse to the file. That covers shortcuts to programs and folders. A website shortcut (a .url file) has no Shortcut tab; its Change Icon… button is on the Web Document tab instead.
In an app or installer. Desktop app frameworks and installer builders commonly ask for an .ico for the application icon. A four-size file like this one covers the sizes they typically need.
How Transparency and Non-Square Images Are Handled
Transparency is preserved. A logo on a transparent background becomes an icon on a transparent background, and it sits cleanly on a dark taskbar, a light Explorer window or a colored browser tab.
Icons are always square. If your PNG is wider than it is tall (or the other way round), the converter scales it to fit inside the square and centers it. The leftover space on the sides is transparent. Nothing is cropped and nothing is stretched. The trade-off is that a wide logo ends up small inside the icon. If you want the mark to fill the whole square, crop the PNG to a square around the part that matters before converting. For favicons that usually means the logo’s symbol rather than the full wordmark.
Very small sizes are where icon artwork usually runs into trouble. Fine lines and small text that read well at 256 pixels can blur into a smudge at 16. The converter downsizes in several steps rather than one to keep edges as clean as it can, but no scaler can make a detailed illustration legible at 16×16. Simple, bold shapes survive best.
How This Converter Works
Upload-based converters such as CloudConvert, Convertio and FreeConvert send your image to a server, convert it there, and send the result back. pixconv.io does the whole job inside your browser:
- Your browser decodes the image locally into raw pixels.
- The image is scaled to 16, 32, 48 and 256 px, stepping down gradually so small sizes don’t turn jagged.
- Each size is encoded as a PNG with its transparency intact.
- The four PNGs are packed into a single
.icofile, which downloads straight from your machine.
Because nothing is uploaded, there’s no queue and no daily limit, and unreleased logos or client artwork never pass through a third-party server. You can convert up to 100 images in one batch.
Quality settings don’t apply here. Every size is stored losslessly, so the only change to your artwork is the resizing itself.
Step-by-Step Guide
Step 1: Add your PNG files.
Drag and drop one or more .png files into the drop zone, or click “Browse files”. Up to 100 files fit in one batch.
Step 2: Let the icons build.
Each image is converted automatically into a four-size .ico. There are no settings to adjust.
Step 3: Download. Click Download next to each file, or Download all as ZIP for a batch.
PNG vs ICO: A Quick Comparison
| PNG | ICO | |
|---|---|---|
| Images per file | One | Several sizes of the same icon |
| Transparency | Yes | Yes (stored as PNG inside) |
| Maximum size | No practical limit | 256×256 per image |
| Used for | Web images, screenshots, graphics | Windows icons, favicon.ico |
| Opens in | Every image viewer and editor | Windows, browsers, icon editors |
Keep the PNG as your master copy. It can be any size and every editor opens it. Generate the ICO from it whenever you need an icon.
Tips for Best Results
- Start big and square. A square PNG of at least 256×256 gives the largest icon size real detail to work with. A smaller source is scaled up for the 256 px version and will look soft.
- Simplify for the small sizes. Check how your icon looks at 16 px in a browser tab. If it’s unreadable, a simplified mark (a single letter, a symbol) often works better than the full logo.
- Use transparency deliberately. A transparent background adapts to light and dark surroundings. A solid square background gives you a consistent tile instead.
- Need a plain image instead? For a PNG at a specific pixel size, use the resize option on JPG to PNG or WebP to PNG.