Some older Windows programs read nothing but .bmp. This converter writes an uncompressed bitmap from your PNG without uploading anything.
Almost nothing modern wants BMP, and yet the requests keep coming: industrial control panels, point-of-sale terminals, embedded display firmware, machine-vision software, and in-house Visual Basic or Delphi applications written before PNG decoding was a given. Those programs read raw bitmaps because raw bitmaps need no decoder at all. If a piece of equipment or a decades-old tool rejects your PNG, converting it is usually faster than arguing with the vendor.
The output is an uncompressed 32-bit BMP: a short header followed by raw pixel rows, bottom to top, four bytes per pixel. Nothing is compressed and nothing is resized, so the file size is pure arithmetic — width times height times four, plus the header. A 64×64 image lands around 16 KB no matter how small the PNG was, and a 1920×1080 screenshot comes out near 8 MB. Growing by an order of magnitude is normal here and is not a sign that something went wrong.
PNG transparency does not survive in a form old software understands, so transparent areas are flattened onto a white background before the bitmap is written — left alone they would come out black in most readers. Keep that in mind for logos with cut-out backgrounds. Because BMP costs so much in file size and gives nothing back in quality, it is only worth producing when something on the other end genuinely demands it; for storage, sharing, or the web, the PNG you already have is the better file. Conversion runs in a Web Worker on your device, batches move three at a time, and results download individually or as a ZIP.
Because BMP stores every pixel raw with no compression, while PNG compresses losslessly. The output size depends only on the image dimensions, not on how well the picture compresses.
No. Both formats keep every pixel exactly, so the picture is unchanged. The only thing lost is transparency, which is flattened onto white.
They are filled with white before the bitmap is written. Left as-is they would render black in most BMP readers, which is rarely what anyone wants.
No. The PNG is decoded and the BMP written inside your browser, so even a large batch never touches the network.