JPG to BMP Converter
Convert JPG photos to Windows BMP bitmaps — uncompressed pixel data with a 54-byte header, the format that everything can read and nothing can compress. Choose 24-bit for maximum compatibility or 32-bit when a tool insists on an alpha channel. The encoder is written out byte by byte in this page, so nothing is uploaded and no external library is involved.
Drop JPG files here
JPG / PNG / WebP accepted · multiple allowed · output is BMP
How to convert JPG to BMP
- Drop your JPGs in (PNG and WebP work too).
- Leave the depth on 24-bit unless the software you are feeding has asked for 32.
- Click Convert to BMP. Expect the output to be many times larger than the input — that is normal for an uncompressed format.
What is inside the file
A 14-byte file header, a 40-byte BITMAPINFOHEADER giving dimensions and bit depth, then the pixels. Two details trip people up when they write their own parsers: BMP stores rows bottom-up, so the first row of pixel data is the bottom of the image, and each row is padded to a multiple of four bytes. Both are handled here. Colour order is BGR, not RGB — another classic source of blue-looking faces in home-made decoders.
Getting the size down
You cannot compress a BMP, so the only variable is how many pixels it contains. Halving the dimensions quarters the file. If the destination has a memory limit — an embedded display, a microcontroller — decide the exact pixel dimensions first with Resize JPG, then convert. For archiving or print handoff where you want lossless and sensible file sizes, TIFF is the better target, and plain PNG is lossless with real compression.
FAQ
Why would anyone want a BMP in 2026?
Because something in the chain cannot decode anything else. BMP is raw pixels behind a 54-byte header, so it turns up wherever a decoder would be a liability: embedded displays and e-paper panels, microcontroller firmware, industrial machines, older test equipment, Windows wallpaper and icon tooling, some CNC and embroidery software, and university assignments that ask you to parse an image format by hand.
How much bigger will the file be?
Dramatically bigger — BMP applies no compression at all. Width × height × 3 bytes, plus a small header: a 12 megapixel photo becomes about 36 MB regardless of how small the JPG was. That is not a bug, it is what "uncompressed" means. If the target has a size limit, resize the image before converting, because pixel count is the only lever.
Should I pick 24-bit or 32-bit?
24-bit unless you have been told otherwise — it is the universally-readable variant, and JPEG has no transparency to preserve anyway. 32-bit adds an alpha byte per pixel (fully opaque here) and is what some newer Windows APIs and game tooling expect. It is written with BI_BITFIELDS masks rather than a BITMAPV4 header, because the V4/V5 variants are rejected outright by macOS.
Will converting improve the quality?
No. BMP is lossless, but it can only be lossless about the pixels it is given, and those pixels already went through JPEG. Every compression artefact in the source is copied faithfully into a much larger file. Converting to a lossless format prevents further loss — useful before heavy editing — but it cannot undo what has happened.
Is anything uploaded?
No. The BMP header and pixel rows are assembled byte by byte in JavaScript inside this page — no library, no server. You can watch it work with the network disconnected.