Which icon sizes should the ICO include?

The working set is 16, 32, and 48 pixels — tabs, taskbar, and Explorer respectively — plus 256 for modern high-DPI contexts. Windows selects the closest match per situation, which is why a proper ICO bundles several renditions rather than one.

How do I get transparent corners when BMP has no alpha?

Classic Windows icons solved this with a separate 1-bit mask, but the practical modern route is different: open the BMP in an editor, delete the background to create transparency, export as PNG, and build the ICO from that. Straight BMP conversion yields a solid square icon.

Does the source bitmap need to be square?

It should be — icon slots are square, so non-square art gets padded or distorted to fit. Crop to a 1:1 composition around the main shape before converting, keeping some margin so the mark doesn't touch the icon edges.

BMP to ICO Converter – Free & Online

Convert BMP to ICO

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Classic Windows icon authoring started from bitmaps, and BMP to ICO conversion still turns square bitmap art into multi-size icon files today. The ICO format even stores its images internally as bitmap data, so the mapping is natural.

Convert BMP to ICO – Free Online BMP to ICO Converter

Why convert BMP to ICO?

Compile desktop and shortcut icons for Windows apps from artwork drawn in Paint or legacy editors.
Produce favicon.ico for retro-styled sites straight from pixel-perfect bitmap sources.
Regenerate icons for old software whose original .ico resources were lost.

Tip: BMP has no transparency, so your icon gets a solid square background — for cutout edges, add alpha in an editor and export PNG before building the ICO.

How to convert BMP to ICO

Upload your BMP file using the area above.
ICO is preselected as the target format.
Click Start and wait for the conversion to finish.
Download your converted ICO file.

Convert BMP to ICO

Convert BMP to ICO – Free Online BMP to ICO Converter

Why convert BMP to ICO?

How to convert BMP to ICO

BMP to ICO — Frequently Asked Questions