What is the ICO format?

ICO is the standard icon format for Microsoft Windows. What makes it special is that a single ICO file can contain multiple versions of the same image at different sizes and color depths — for example, 16×16, 32×32, 48×48, and 256×256 pixels. Windows automatically picks the sharpest version for each situation, so your icon looks crisp whether it appears in a tiny taskbar or a large desktop shortcut. ICO files are also the classic format for website favicons, the little icons shown in browser tabs.

When should you use ICO?

Use ICO whenever you need icons for Windows software, desktop shortcuts, or app installers. It is also the traditional choice for favicons, although modern browsers now accept PNG favicons too. If you are designing an app, a website, or any Windows program and want a professional icon that stays sharp at every size, ICO is the format to reach for.

Key benefits of converting to ICO

The multi-size container is ICO's killer feature: instead of managing a dozen separate icon files, you ship one ICO that covers every display size, from small list views to high-DPI monitors. Icons stay pixel-sharp because the operating system selects the closest matching size rather than scaling a single image. ICO also supports transparency, so icons blend cleanly into any desktop background or browser tab.

How to convert your images to ICO

FlowTool creates professional ICO files from any image in seconds, completely free. Upload your source image with the Browse Files button or drag it into the upload area, then press Convert. The icon is generated right in your browser with multiple embedded sizes, ready to download — no signup, no watermark, no software to install.

Tips for the best results

Start with a square, high-resolution source image — at least 256×256 pixels — so every embedded icon size looks sharp. Simple, bold designs read best at tiny sizes, so avoid fine text or intricate detail in your icon artwork. For website favicons, place the ICO file at your site's root and reference it in your HTML head, and it will appear in browser tabs and bookmarks automatically.