AVIF to BMP converter

AVIF stores a picture the way video is stored. The Alliance for Open Media took the AV1 codec and wrote down, in the AV1 Image File Format specification, how to keep a single frame of it inside an image file; version 1.2.0 of that document is dated 16 October 2025.[1] That is where its weight comes from: the MDN guide puts an AVIF file at roughly half the size of a JPEG at comparable quality.[2]

BMP keeps every pixel whole and applies no compression. Microsoft defined it as a device-independent bitmap, a way to move a picture between machines and programs, and that is the job it has held ever since.[3] The layout takes a few sentences to describe: a header with the file size, a second header with the dimensions and the number of bits per pixel, and behind them the raw array of points.[4]

That plainness is exactly why BMP is still needed. Reading such a file takes no library, and a program written thirty years ago will make sense of it. The MDN guide adds the fair warning that this same weight rules the format out for web pages.[2]

Drag your AVIF files onto the Add files area, or click it and pick the images from your drive. Then press the Convert button. You can download the finished bitmaps one at a time with the Download button on each queue row, or all at once with Download all.

The quality here is fixed at the highest it can be. BMP keeps pixel values whole, so whatever the browser read out of the AVIF lands in the output file: the same pixel count and the same colours.

The result is written as 24-bit with a BITMAPINFOHEADER, one byte each for red, green and blue. This is the oldest and most widely read shape of the format, accepted by every program that opens BMP at all. The rows run from the bottom of the image upwards, the way the vast majority of programs write them.

In the queue on the right, every file shows its weight before and after conversion together with the difference in per cent. The same summary for the whole batch sits under the buttons, on the Increased line. Clear all empties the queue, and the Remove label on a row takes a single file out of it.

All the work happens on your own machine. The page code loads the AVIF file, draws it on a browser canvas and assembles the bitmap from there byte by byte. The image stays on your device from the first click to the end of the job and leaves the browser's memory once you close the tab.

Under the converter sits a format switch reading AVIF to BMP. Clicking either of the two formats opens a list, and picking from it takes you to the converter page for that pair. Every pair in this group is also gathered on the Format conversion page.

You know the weight of the finished BMP before you press Convert, because it depends on the dimensions of the image alone. Every pixel takes three bytes. Every row is padded with zeros up to a full four bytes; the Microsoft documentation gives the formula for it.[5] To all the rows together you add 54 bytes of header.

Let us walk through a photo measuring 3000 by 2000 pixels. One row is 3000 pixels at three bytes each, which is 9,000 bytes. At this width the padding comes out at zero. There are 2000 rows, so the pixels alone take 18,000,000 bytes. With the header that gives 18,000,054 bytes, which is 17.2 MB in the notation the tool uses in its summary.

The row padding only shows up at widths that do not divide by four. An image 801 pixels wide needs 2,403 bytes for a row and will still take 2,404 bytes in the file. That single byte comes back on every row, so across a thousand rows it grows into a kilobyte.

The same arithmetic applies to every picture. A photograph full of detail and a plain white board of the same dimensions produce a file of the same size, because BMP in this flavour keeps every point separately. Going the other way the relationship is reversed, and the table on the BMP to AVIF converter page shows it: there the weight of the result depends mostly on how many flat areas the image holds.