BMP vs ICO
A detailed comparison of BMP Image and ICO Icon — file size, quality, compatibility, and which format to choose for your workflow.
BMP Image
Raster & Vector ImagesBMP is an uncompressed raster image format native to Windows. Files are large but preserve exact pixel data with no compression artifacts. Rarely used on the web due to file size.
About BMP filesICO Icon
Raster & Vector ImagesICO is the icon file format used for favicons and Windows application icons. A single ICO file can contain multiple image sizes and color depths for different display contexts.
About ICO filesStrengths Comparison
BMP Strengths
- Dead-simple format — trivially easy to read and write.
- Lossless and uncompressed — perfect bit-exact pixel storage.
- Universally supported in Windows applications since 1985.
- Supports 1, 4, 8, 16, 24, and 32-bit color depths.
ICO Strengths
- Multi-resolution: one file, many sizes, OS picks the right one.
- Universal favicon support in every browser since IE5.
- Supports transparency (1-bit since 1985, full alpha since XP).
- Tiny file size — an entire favicon pack typically fits in under 15 KB.
- No licensing or patent concerns — fully in the public domain spec-wise.
Limitations
BMP Limitations
- Enormous file sizes — no meaningful compression in typical use.
- Not a web format — browsers support it but nobody serves BMPs over HTTP.
- No metadata support (no EXIF, no ICC profile in practice).
- Multiple header versions mean "a BMP" is ambiguous — parsers must handle several variants.
ICO Limitations
- Cannot compress continuous-tone images efficiently — use PNG or WebP for photos.
- Format is essentially frozen in 1999 — no HDR, no wide gamut, no modern features.
- Maximum image dimension is 256×256 px (inside an ICO container).
- Editing requires specialized tools — most image editors treat it as a curiosity.
Technical Specifications
| Specification | BMP | ICO |
|---|---|---|
| MIME type | image/bmp | image/vnd.microsoft.icon |
| Extensions | .bmp, .dib | — |
| Compression | None (typical); RLE 4/8 bit (rare) | Uncompressed bitmap or embedded PNG (Vista+) |
| Color depths | 1, 4, 8, 16, 24, 32 bits per pixel | 1, 4, 8, 24, 32 bits per pixel |
| Byte order | Little-endian | — |
| Max resolutions per file | — | 65 535 images |
| Max single image size | — | 256×256 px |
Typical File Sizes
BMP
- Small icon (32×32) 4 KB
- Screenshot (1920×1080) ~6 MB
- 4K image (3840×2160) ~25 MB
- Scanned A4 at 300 dpi ~25 MB
ICO
- Classic favicon (16×16 only) < 2 KB
- Multi-size favicon pack (16/32/48/256) 5-15 KB
- Full Windows app icon set 20-100 KB
Ready to convert?
Convert between BMP and ICO online, free, and without installing anything. Encrypted upload, automatic deletion after 2 hours.
Frequently Asked Questions
BMP (Bitmap) is a raster image format developed by Microsoft for Windows. It stores images with no compression by default, resulting in large file sizes but pixel-perfect quality. It has been part of Windows since version 1.0.
ICO (Icon) is Microsoft's 1985 multi-resolution icon format, originally shipped with Windows 1.0. A single .ico file holds multiple sizes (16×16, 32×32, 48×48, 256×256) so the OS can pick the best one for the current display context. Since 1999, every website uses a favicon.ico to show its icon in browser tabs.
BMP files open in Windows Paint, Photos, macOS Preview, GIMP, Photoshop, and virtually any image viewer. All Windows applications support BMP natively.
On Windows, ICO files open natively in File Explorer and Photos. On macOS, Preview handles basic display. For editing, use GIMP (free), Photoshop with a plugin, or dedicated icon editors like IcoFX.
PNG is better than BMP in almost every scenario since it provides lossless compression (smaller files), transparency support, and wider cross-platform use. BMP is mainly relevant for legacy Windows applications.
Use the PNG-to-ICO converter on KaijuConverter — upload a PNG (ideally square, at least 256×256) and download a multi-resolution ICO with all standard favicon sizes embedded.