How to Convert BMP to ICO: Step-by-Step Tutorial

By Bill Crawford  ·  March 2026  ·  6 min read  ·  Last updated March 6, 2026

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What This Tutorial Covers

This tutorial walks you through converting BMP bitmap images to ICO format using the browser-based tool on this site. No software installation required. You will learn how to add files, understand the per-file status system, use batch ZIP download, and deploy your ICO as a favicon.

For background on why you might want ICO and when to use it, see the companion BMP to ICO Complete Guide.

What You Need

• One or more .bmp files (Windows bitmap images)
• A modern browser: Chrome, Edge, Firefox, or Safari (2022 or later)
• No account, no software, no subscription

Step 1: Open the Converter

Navigate to dataconversioncenter.com/image-tools/bmp-to-ico/. The page loads JSZip from CDN for ZIP packaging — no other external libraries are needed because BMP is natively supported by all modern browsers. The ICO encoder is written in pure JavaScript and runs entirely in your browser.

Step 2: Add Your BMP Files

You have two ways to add files:

• Drag and drop: Open your file manager and drag one or more .bmp files directly onto the drop zone labeled "Drop BMP files here". The zone highlights in blue when you hover over it.
• Browse: Click anywhere on the drop zone (or the "Browse Files" link) to open your file picker. Select multiple files using Ctrl+click (Windows) or Cmd+click (Mac).

As soon as files are added, the tool generates thumbnail previews for each one. You will see an Input Files grid with a card per file showing the filename, file size, and a Ready status badge.

Note: Files with an extension other than .bmp are automatically rejected with an inline error message. They are not added to the conversion queue.

Step 3: Choose Download Mode

Before converting, decide how you want to download your ICO files:

• Individual downloads (default): Leave "Download as ZIP" unchecked. After conversion, each output card has its own Download button, and a "Download All ICOs" button appears for sequential bulk download.
• ZIP archive: Check "Download as ZIP". After conversion, a single "Download ZIP" button downloads all ICOs in one file named dataconversioncenter_bmp_to_ico_YYYYMMDDHHMM.zip using your local date and time.

For batches of more than 5 files, the ZIP option is strongly recommended to avoid multiple browser download dialogs.

Step 4: Click "Convert to ICO"

Click the blue Convert to ICO button. The button label changes to "Converting…" and is disabled while conversion runs.

For each file in sequence:

1. The status badge on the input card changes from Ready to Converting…
2. The browser decodes the BMP natively using its built-in image engine — no external library needed.
3. The pixel data is drawn to an HTML Canvas element at full resolution.
4. The canvas is scaled to six sizes: 16, 32, 48, 64, 128, and 256 pixels square.
5. Each scaled canvas is encoded as a PNG blob.
6. All six PNG blobs are assembled into a standards-compliant ICO binary with a proper ICONDIR header and ICONDIRENTRY table.
7. The status changes to Converted and an output card appears.

The progress bar tracks overall progress — "Converted X of N". Files are processed two at a time for throughput efficiency.

Step 5: Review the Results

After conversion completes, a summary banner appears: "✓ All N files converted successfully" or "Completed: X succeeded, Y failed."

An Output Files grid displays cards for each successfully converted ICO, showing:

• A thumbnail preview (the full-resolution source rendered for display)
• The output filename — same base name as the input with .ico extension (e.g. logo.bmp → logo.ico)
• Output file size (typically 50–300 KB for a 6-size ICO)
• A per-file Download ICO button

Any files that failed to convert are marked with a red Error badge. Common causes: the file is corrupted, has an unusual BMP variant the browser cannot decode, or the browser ran out of memory on an extremely large file.

Step 6: Download Your ICOs

Individual download

Click the ⬇ Download ICO button on any output card to save that file. The filename is the same as the input with .ico extension.

Download All (no ZIP)

With "Download as ZIP" unchecked, click Download All ICOs. The tool triggers sequential browser downloads with a 120 ms delay between each to prevent browser throttling.

Download ZIP

With "Download as ZIP" checked, click Download ZIP. JSZip assembles all ICO blobs in memory and downloads a single file named, for example, dataconversioncenter_bmp_to_ico_202603061200.zip.

Step 7: The Tool Resets Automatically

After a ZIP download or "Download All" completes, the tool automatically resets to its initial empty state. All thumbnails, cards, and file references are cleared. The checkbox resets to unchecked. This prevents accidental re-downloads and keeps browser memory clean between sessions. Click Start Over to reset manually at any point.

Bonus: Deploy as a Favicon

If your goal is a website favicon, here is what to do after downloading the ICO:

1. Rename the file to favicon.ico.
2. Upload it to the root directory of your web server (the same level as index.html).
3. Add this to your HTML <head>: <link rel="icon" href="/favicon.ico" sizes="48x48">
4. Clear your browser cache and reload — the new favicon should appear in the browser tab.

For high-DPI displays, also add an SVG or 32×32 PNG favicon alongside the ICO for the sharpest rendering on Retina screens.

Troubleshooting

• File shows Error status: Verify the file is a valid BMP. Some files renamed to .bmp may actually be in a different format. Try opening it in Paint or another image editor to confirm it is a genuine BMP.
• Large BMP takes time to preview: Very large BMP files (over 20 MB) may take a few seconds to decode the preview. The thumbnail will appear when ready; conversion will proceed normally.
• ICO looks blurry at 16px: This means the source BMP has too much fine detail for small sizes. Use a simpler, higher-contrast source image with a bold centered subject.
• ZIP not downloading: Some browsers require a direct user interaction to trigger downloads. Ensure you clicked the Download ZIP button directly without any intervening popups.
• Only some files converted: Files that fail are skipped and marked Error. The remaining files in the batch convert normally. Check the error message on the failed card for details.

Next Steps After Conversion

• Deploy as favicon: Follow the steps above to place favicon.ico in your web root.
• Use in Windows app: Add the ICO file to your Visual Studio or IDE project as an application icon resource.
• Convert to modern web format: Use BMP to AVIF if you need a compressed web-friendly version of the same bitmap.
• Resize for other targets: Use Image Resizer to scale the source to specific social media or app store icon dimensions before converting.
• Compress for storage: Use Image Compressor to reduce file size if you also need a web-optimized version of the original graphic.

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