Skip to content
ImageConverter

Secure server conversion

BMP to ICO Converter

Convert a BMP into a Windows ICO icon containing 16, 32, 48 and 256 pixel versions. These two formats are more closely related than any other pair on this site — an ICO has always been, in essence, a container full of bitmaps.

Deleted automatically Uploads removed within 30 minutes

Drag and drop your BMP images here

Add several at once. Each file is processed and then deleted from our server.

Up to 20 MB per file Batch ready

Step by step

How to convert BMP to ICO in 3 steps

  1. Add your BMP

    Old files are fine; they usually convert without complaint.

  2. Nothing to configure

    Each standard size is written into one file.

  3. Download your .ico

Format comparison

BMP vs ICO

BMP (Windows Bitmap)

Uncompressed

An early Windows format that stores pixels more or less raw, with little or no compression.

  • Read by old and embedded software that knows nothing newer
  • No compression artefacts
  • Very large files for the image size

ICO (Windows Icon)

Multi-size icon

Bundles several sizes of the same small image in one file, for Windows icons and website favicons.

  • Several icon sizes in a single file
  • Understood by every browser as a favicon
  • Only for small images — each entry is at most 256 × 256 pixels

The same family

ICO and BMP both come from mid-1980s Windows, and the relationship is not merely historical: the images stored inside an ICO file have traditionally been device-independent bitmaps — BMP data, minus its file header. Open an old icon in a hex editor and you are looking at bitmap structures.

That is why this conversion is so untroubled. There is no colour model to reconcile, no compression scheme to translate. The pixels are already in the form the container wants.

Modern icons commonly store the larger sizes as PNG instead, because a 256×256 uncompressed bitmap is a megabyte and a PNG of the same thing is a fraction of that. The container permits both, and readers have handled PNG entries for many years.

Transparency: the one thing BMP cannot give you

ICO has supported transparency since the beginning — originally through a separate one-bit mask, later through a full alpha channel.

BMP, in every version you are realistically going to encounter, does not. A 32-bit BMP with an alpha channel is technically possible and almost never what you have; what you have is a solid rectangle, background included.

So your icon will have whatever background the bitmap had — usually white or magenta, since older tools used bright magenta as a stand-in for "transparent". That looks obviously wrong on a browser tab. If your artwork needs transparency, save it as a PNG with a genuine alpha channel first and use PNG to ICO.

Non-square bitmaps are padded

A non-square source is centred on a square canvas rather than stretched, so proportions are preserved. As with the background above, that padding is filled rather than transparent when the source has no alpha to inherit.

Quality

Quality and file size

There is no quality setting — each size is stored losslessly, and BMP had nothing lossy to begin with.

Old bitmaps and low colour depths

BMPs are frequently old, and old bitmaps are often 16 or 256 colours rather than the 16 million a modern image has. Those convert perfectly well, and an icon is one of the few places a limited palette genuinely does not matter: at 16 pixels nobody is counting colours.

Occasionally a very old file will not convert at all — usually a 16-bit variant with unusual channel masks, or an OS/2 header. Opening it in any modern editor and saving it as PNG normalises it.

The magenta problem

If your bitmap has a bright magenta or cyan background, that was almost certainly meant as a transparency key — an old convention where a specific colour meant "do not draw this". Nothing today honours it automatically.

Remove that background in an image editor and save as PNG with real transparency before making an icon, or you will ship a logo on a magenta square.

Start at 256 pixels

Sizes larger than your source are skipped rather than upscaled, so a small bitmap yields a smaller icon rather than a blurry one. Since BMPs are uncompressed, a 256-pixel source is only about 260 KB — there is no reason to start small.

Where this comes up

  • Legacy Windows software being modernised, where the original artwork exists only as BMP.
  • Old application icons extracted from resources and needing to be rebuilt.
  • Classic Paint files, since Paint saved BMP by default for decades.
  • Industrial and embedded systems, which still emit BMP because the format is trivial to write.
  • Installers, which want an ICO and are often built alongside BMP assets.

Why ICO holds several sizes

A single icon file carries the same artwork at multiple resolutions so that whatever displays it picks the closest match instead of scaling. A browser tab takes the 16, a desktop shortcut the 48, a large tile the 256.

That idea was ahead of its time in 1985 and is the main reason the format is still in use. Every other icon system since has copied it.

Where the file goes

For a website, name it favicon.ico and put it at the site root — browsers request /favicon.ico without being told to. For a Windows application, the ICO is referenced from the resource file or the installer script.

Going the other way

ICO to BMP extracts the largest image from an icon as a bitmap, which is useful when working with older tooling that expects BMP. For anything modern, ICO to PNG is the better choice — it keeps transparency, which BMP cannot.

What happens to your file

Browsers cannot write the ICO container, so this runs on our server. Your upload is deleted the moment conversion finishes, the result is deleted as you download it, and anything abandoned is swept automatically.

Privacy

What happens to your file

This tool runs on our server, so it works the same on every phone and computer. Your file is uploaded, and this is exactly what happens to it:

  • Stored outside the public web root under a random name, never under your file's name.
  • Processed, with the original upload deleted immediately — whether it succeeded or failed.
  • The result sits behind a signed link that only you receive, which stops working after 20 minutes, and the file is deleted the moment you download it.
  • Anything never collected is deleted automatically within 30 minutes.
  • The image itself is never logged or kept. If a conversion fails, we record the formats involved and the error — not the file.
  • Camera metadata, including any GPS coordinates recording where a photo was taken, is removed from the result. Only the rotation needed to show the image the right way up is kept.

Questions & answers

BMP to ICO: frequently asked questions

Are BMP and ICO related?

Closely. Both come from mid-1980s Windows, and the images inside an ICO have traditionally been device-independent bitmaps — BMP data without its file header. That is why the conversion is so untroubled: there is no colour model to reconcile and no compression to translate. Modern icons often store larger sizes as PNG instead, since a 256×256 uncompressed bitmap is about a megabyte.

Why does my icon have a background?

Because BMP has no usable transparency. ICO has supported it since the beginning, but a bitmap has none to give — so whatever background the image had comes with it. Save your artwork as a PNG with a real alpha channel and convert that instead.

My bitmap has a magenta background. What is that?

An old transparency convention, where a specific bright colour meant "do not draw this". Nothing today honours it automatically, so you will ship a logo on a magenta square. Remove the background in an editor and save as PNG with real transparency before making an icon.

Will a 256-colour bitmap work?

Perfectly. An icon is one of the few places a limited palette genuinely does not matter — at 16 pixels nobody is counting colours.

My very old BMP will not convert.

Probably a 16-bit variant with unusual channel masks, or an OS/2 header. Bottom-up row order, low colour depths and RLE compression are all handled. Opening it in any modern editor and saving as PNG will normalise it.

How large should the source be?

256 pixels square. Sizes larger than your source are skipped rather than upscaled, so a small bitmap gives a smaller icon rather than a blurry one — and since BMP is uncompressed, a 256-pixel source is only around 260 KB anyway.

Keep going

Related image tools

View all tools

PNG to ICO Converter

Convert PNG to a proper multi-size ICO containing 16, 32, 48 and 256 pixel versions. Transparency preserved.

On our server

ICO to BMP Converter

Extract an ICO to BMP for legacy tooling. Counter-intuitively the closest format is the one that discards the most — here is why.

On our server

Favicon Generator

Generate a full favicon set from one image: multi-size ICO, Apple touch icon, Android icons, manifest and the HTML to paste in.

On our server

BMP to PNG Converter

Convert BMP to PNG with no quality loss at all. Typically 70-90% smaller, and perfect for screenshots and pixel art.

On our server