CONVERT
ICO → AVIF
Fast, secure ICO to AVIF conversion. No registration required.
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ICO is the Windows icon container with multiple resolutions packed into one file. Reaching a AVIF from there is one hop. If you have ended up with a ICO and need a AVIF, the mismatch is almost always about where the image is going next rather than the picture itself. Our server reads the ICO with ImageMagick, decodes each pixel, and re-writes it as a AVIF using defaults tuned for fidelity first and file size second. Worth knowing: ICO is the Windows icon container with multiple resolutions packed into one file. Meanwhile AVIF is the AV1-based next-gen image codec, extremely efficient with full HDR and alpha support.
ICO Icon
Source formatICO 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.
AVIF Image
Target formatAVIF is a next-generation image format based on the AV1 video codec. It offers significantly better compression than JPEG and WebP while maintaining excellent visual quality, including HDR and wide color gamut support.
Why convert ICO to AVIF
Both ICO and AVIF describe a grid of pixels — the difference lies in how that grid is compressed, whether transparency is supported, and which software opens it natively. Moving from ICO to AVIF is worth it when the AVIF ecosystem is broader for your use case, or when AVIF compresses photographs more efficiently than ICO.
HOW TO CONVERT
ICO → AVIF
Drop the ICO file
Drag and drop or click to upload your ICO. The image is transferred securely over HTTPS and queued for conversion.
Re-encode with ImageMagick
ImageMagick decodes every pixel of the ICO and writes a matching AVIF with sensible default quality settings.
Download the AVIF
The converted AVIF is ready to download as a single file; both files delete automatically within two hours.
Common Use Cases
Web publishing and CMSes
AVIF uploads cleanly to WordPress, Ghost, Webflow and most blogging platforms; many CMSes silently transcode or reject ICO.
Email attachments
Email clients preview AVIF inline while ICO may arrive as an unrecognised attachment on older Outlook or mobile apps.
Social media uploads
Platforms like Instagram, X and Facebook accept AVIF natively; ICO is often rejected or silently converted with unpredictable results.
Design hand-off
Designers shipping assets to developers prefer AVIF for faster pipeline imports and consistent display across build tools.
ICO vs AVIF — Strengths and limitations
What each format does best, and where it falls short.
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
- 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).
AVIF Strengths
- Best-in-class compression efficiency — 30-50% smaller than JPEG for the same quality.
- Royalty-free and patent-unencumbered (unlike HEIC).
- Supports alpha transparency, HDR, wide gamut (BT.2020), and up to 12-bit color.
- Progressive decoding: a blurry preview appears while the file is still downloading.
- Supported in all major browsers since late 2022 — no polyfills needed.
Limitations
- Encoding is CPU-expensive — an AVIF export can take 10-30× longer than JPEG.
- Older software (pre-2022) cannot open AVIF without plugins.
- Email clients still largely ignore it — stick to JPEG for attachments.
ICO vs AVIF — Technical specifications
Side-by-side comparison of the technical details.
| Specification | ICO | AVIF |
|---|---|---|
| MIME type | image/vnd.microsoft.icon | image/avif |
| Max resolutions per file | 65 535 images | — |
| Max single image size | 256×256 px | — |
| Color depths | 1, 4, 8, 24, 32 bits per pixel | — |
| Compression | Uncompressed bitmap or embedded PNG (Vista+) | — |
| Container | — | HEIF (ISOBMFF) |
| Codec | — | AV1 (intra-only) |
| Max dimensions | — | 65 536 × 65 536 px |
| Color depth | — | Up to 12-bit per channel |
| Color spaces | — | sRGB, Display-P3, BT.2020, arbitrary ICC |
ICO vs AVIF — Typical file sizes
Approximate file sizes for common scenarios.
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
AVIF
- Thumbnail (400px) 10-30 KB
- Web photo (1920px) 80-300 KB
- 4K photo (3840px) 300 KB - 1.2 MB
- Lossless copy of 24MP photo 8-15 MB
Quality & Compatibility
If AVIF is a lossless format (PNG, TIFF, BMP) the output keeps every pixel of the decoded ICO exactly. If AVIF is a lossy codec (JPEG, WebP, HEIC), the encoder re-compresses the image at the quality level you select — default 85 is transparent for photographs, quality 92+ for illustrations with hard edges.
Tips for Best Results
- Keep the original ICO alongside the AVIF output — re-encoding already-lossy images accumulates detail loss on each round.
- If the AVIF will be uploaded to a CMS, check whether the platform has a max dimension and downscale once on export rather than letting the CMS resize automatically.
- For thumbnails and avatars, export the AVIF at exactly the display size; browsers will otherwise resample and the image may look soft.
Frequently Asked Questions
Frequently Asked Questions
It depends on the codecs involved. If both ICO and AVIF are lossy, the pixels are re-encoded and a small amount of detail is discarded — invisible at default quality settings on photographs. If AVIF is lossless (PNG, TIFF, BMP) the output keeps every pixel of the decoded ICO exactly, but cannot recover detail that ICO had already compressed away.
Often yes, especially when AVIF is lossless. ICO tuned for efficient web delivery will usually produce smaller files than AVIF's default settings. If file size matters, drop the quality in Advanced or pick a more compressed target format instead.
KaijuConverter uploads over HTTPS, processes the image in an isolated container and deletes both the source and the output within two hours. No account is required, file contents are never logged, and we do not use uploads to train any model. For confidential material, the paid plan includes a data-processing agreement.
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Your files are encrypted during transfer, processed in isolated containers, and automatically deleted within 60 minutes. We never read, share, or store your data.