BMP files: why they are so large and what to use instead

What BMP is

BMP, or Windows Bitmap, is a simple image format that Microsoft introduced for Windows. It stores a color value for each pixel, usually with no compression, so the program reading it has very little to decode.

Why the files are so big

In a 24 bit BMP every pixel takes three bytes. A picture of 1920 by 1080 pixels is therefore about 6.2 MB, and a 12 megapixel photo of 4000 by 3000 pixels is about 36 MB. The size depends only on the pixel count, not on how simple the picture is, so a plain white image is as large as a detailed photograph.

What to use instead

• PNG for screenshots, drawings and text. It is lossless, so the picture stays identical, but the file is usually far smaller, especially for flat colors.
• JPG for photographs. It is lossy, and a quality setting around 85 to 90 keeps most photos looking the same while saving a great deal of space.
• WebP when the picture will be used on a website that supports it.

When BMP is still used

Some older programs, embedded devices and simple tools still create or require BMP because it is easy to read and write. In everyday work there is rarely a reason to keep BMP as the final format.

Convert without losing what matters

BMP to PNG is lossless, so every pixel stays the same. BMP to JPG is much smaller for photos but not exact. Both run in your browser, so the picture is not uploaded, and you can convert many files at once and download them together.