THE FILE FIELD GUIDE

.ico

Windows Icon

Images

ICO is an icon format that can hold images of multiple sizes and bit depths. Renaming a PNG is not ICO conversion; inspect how the icon looks at small display sizes.

What it is used for: Windows icons and website favicons
What the file contains: Binary data

All sections, questions and sources

Content reviewed：2026-10-12 · Editor：Kai

Opening steps

Choose your environment or purpose to see its steps.

Windows: use as an icon

Viewing and assigning an icon are separate operations.

Save a trusted ICO locally and inspect it in a compatible viewer.
Use the destination’s Change Icon interface, such as a shortcut’s properties.
Check small-size legibility and keep the referenced file in a stable location.

Image asset: inspect individual sizes

An ICO can contain several images.

Open the file in an ICO-capable editor.
Inspect the available sizes and alpha background, including small images such as 16 px.
Export the required image to PNG and inspect edges and transparency.

Website: use as a favicon

Caching also affects the visible result.

Place the ICO at its intended location and check existing icon references.
Check that the HTML icon URL matches the deployed file and is accessible.
Check another browser and assess search-result changes after recrawling.

Menu labels and support vary by app, OS and version. Preserve the original before making changes.

Troubleshooting by symptom

Blurry small icon: inspect outlines and padding at the actual small sizes.
Solid background: check transparency support and edge behavior against different backgrounds.
Old favicon persists: verify the referenced URL, deployed file and browser cache.
Blurred icon: inspect whether a small embedded image is being enlarged.
White/black fringe: inspect alpha and edge pixels against light and dark backgrounds.
Old website icon persists: verify the reference URL and caching; search results do not necessarily update immediately.

PNG → ICO / ICO → PNG

Open the source in an ICO exporter, choose the required sizes/transparency and save a copy.
When exporting PNG, choose which embedded size to extract; enlargement cannot restore missing detail.
Inspect the exported ICO sizes and check edges/background at the actual small display size.

Renaming is not conversion. Verify that the export contains the intended sizes.

Designing for small icons

Dense lettering becomes illegible when reduced. Inspect actual 16/32 px sizes and prepare simplified small-size artwork.

Different embedded images may be chosen for different contexts; inspecting one is insufficient.

Source for these steps：Microsoft · ICON resource

Favicon deployment and search results

First verify direct access to the icon URL and its HTML reference.

Browser caching and search-engine crawling are separate. Keep a stable URL and inspect both stages.

Source for these steps：Microsoft · ICON resource

Related-format differences

Related-format differences
Format	Main role	Selection notes
ICO	Windows / favicon icon	Inspect sizes and alpha
PNG	Single-image asset	Renaming does not create ICO
SVG	Scalable artwork	Check support for the destination

Handling and security

Do not confuse ICO images with executable files such as SCR. Verify the source and rights to website artwork.

Questions and answers

Can ICO hold only one image?

It can contain multiple sizes and bit depths.

Can I just rename PNG to ICO?

No; use actual ICO encoding/export.

Why has the search-result icon not changed?

Search engines may need time to recrawl; first verify the public URL and icon references.

Can I rename PNG to ICO?

Renaming does not create an ICO structure. Use an ICO-capable exporter.

Can one ICO contain multiple sizes?

Yes. Include appropriate sizes and check readability at the smallest one.

Format facts: name, steward and MIME type

Formal name: Windows Icon file
Steward / specification: Microsoft
MIME type: image/vnd.microsoft.icon

Primary and official sources

Official documentationICON resource
Documents icon resources containing multiple images.
Microsoft · Link checked：2026-10-12
Official documentationIcons (Menus and Other Resources)
Explains icon image groups and their Windows usage.
Microsoft · Link checked：2026-10-08