Resize BMP Images

BMP files are famous for being huge, and you may have one that has to stay a BMP because an old program, a device or a template only accepts that type. The way to make it lighter without changing the type is to reduce its pixels. This resizer does that in your browser and writes a BMP back, with no upload.

Drop images here, click to choose, or paste with Ctrl+V
BMP files · the file type stays the same · many files at once · nothing is uploaded

How to resize BMP images

  1. Add your BMP files by dropping them, clicking the drop zone or pasting.
  2. Choose the new size: a percentage, a maximum width and height, or an exact size. The quick sizes fill in common values.
  3. Press Resize and compare the old and new size of each file. The file type stays the same.
  4. Download each file or all of them as a ZIP.

When to resize, and when not to

  • A device, embedded screen or legacy program only reads BMP and the file is too big or the wrong dimensions.
  • You need the same bitmap at several sizes for a test or a template.
  • A BMP is far larger than it needs to be for the way it is displayed.
  • If the file type does not have to be BMP, the Image Converter can turn it into something far smaller. Do not enlarge a small BMP expecting extra detail.

What changes

  • The file stays a BMP. This tool has no output-type choice.
  • The output is a 24-bit uncompressed bitmap, so its size follows the pixel count directly.
  • BMP has no transparency, so any see-through or empty area is filled with the background colour you pick.
  • There is no quality slider, because BMP stores every pixel without compression.
  • Photo metadata is not written to the new file, and the download is named with its new size, for example scan-800x600.bmp.

Why a BMP shrinks so predictably

This tool writes BMP files without any compression. Every pixel takes the same amount of space, three bytes for its colour, and the rows are padded to fit the format. That means the file size is basically the width times the height times three, plus a small header, and it does not depend on what the picture looks like.

That predictability is useful. Halving both the width and the height leaves a quarter of the pixels, and therefore about a quarter of the file. Because the relationship is so direct, resizing is the only real way to make an uncompressed BMP smaller while keeping it a BMP.

Hitting a file size with a BMP

The Aim for a file size option works well here precisely because the size is so regular. Type a target in kilobytes and the tool reduces the width and height until the file fits, keeping the proportions. There is no quality setting to trade against, so pixels are the only thing that can change.

The note under each result tells you the new dimensions. If you ask for something too small for the picture to survive, the tool keeps the smallest result it could make and says that the target was not reached.

Padding, cropping and the background colour

When you pick Exact size, Fit inside keeps the whole picture and fills the leftover space. Because a BMP cannot be transparent, that space gets the background colour. Choose white for a document scan, black for a screen test pattern, or any colour that matches where the bitmap will be shown.

Fill and crop instead covers the whole rectangle and trims the edges, and Stretch changes the proportions to hit the exact numbers. Percent and Max size keep the proportions without any padding at all, and Max size never enlarges a picture that is already small enough.

Privacy: your files stay on your device

  • The tool decodes, resizes and encodes your pictures with your browser. The files are never sent to a server.

Frequently asked questions

Does my BMP stay a BMP?

Yes. The resizer never changes the file type. A BMP goes in and a BMP comes out. Use the Image Converter when you want a lighter type such as JPG or PNG.

Why is the resized BMP still big?

A BMP written by this tool is uncompressed, so size follows pixel count. Reduce the width and height further, or set a target size and let the tool do it.

What happens to transparency?

BMP cannot store it. Transparent or empty areas are filled with the background colour from the options.

Is there a quality slider for BMP?

No. BMP files are not compressed, so there is nothing to trade. Only the number of pixels changes the file size.

Can I resize many BMP files together?

Yes. They are processed one after another and you can download them all as a ZIP. Very large bitmaps use a lot of memory, so convert fewer at a time on a phone.

Does the tool upload my bitmap?

No. The file is read and rewritten in this browser tab, and nothing is sent to a server.

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