How can a small picture take up so many megabytes as a BMP?

Because a standard bitmap stores three bytes for every pixel and applies no compression at all. That is pure arithmetic rather than an estimate, since a 1920 by 1080 screenshot needs 1920 times 1080 times 3 bytes, which is roughly six megabytes before you have added a single byte of anything interesting.

Does this tool handle a BMP with a transparent background?

It does not attempt to. The module takes the plain conversion route because the bitmaps people actually convert, from Paint, scanners and legacy business software, are opaque. A rare 32-bit BMP with a real alpha channel would not get its transparent areas filled with white the way the PNG converter does, so convert that file to PNG first if transparency is involved.

Which BMP variants can the tool open?

Whatever your browser's own image decoder accepts, which covers the ordinary uncompressed bitmaps that Paint, Windows screenshot tools and scanner software produce. Exotic or malformed variants that the browser refuses will fail with the tool's generic error rather than a specific message about the bitmap header.

Is the quality dial worth touching for a scanned document?

Usually, yes. Scans of text pages are full of sharp black-on-white edges, which is the content JPEG handles least gracefully, so pushing the value above the default of 90 keeps the lettering cleaner. A photograph scanned from a print is the opposite case and copes well at lower settings.

What happens to the filename?

A trailing .bmp is stripped and .jpg is appended, so Untitled.BMP becomes Untitled.jpg. The extension is matched regardless of case and nothing else about the name is altered, which keeps a numbered batch of scanner output in its original order.

Convert BMP to JPG Online Free, Batch, No Upload

Convert Windows BMP bitmaps into far smaller JPG files in your browser. Free, batch, no upload, no size limit and no watermark on the output.

🔒 Private by design: your files are processed locally in your browser and never uploaded to any server.

Converting a pile of bitmaps

Drop your .bmp files onto the box above, or click Choose files. Files from separate drops accumulate into a single batch, and a file already listed under the same name and size is not added again.
Set JPG quality (1–100) if you want something other than 90. A number you type is clamped into that range; a box you clear counts as no value at all, so the conversion falls back to 90 rather than to the lowest quality the encoder offers.
Click Convert BMP to JPG. Each bitmap is decoded and re-encoded in turn, so the progress bar moves one step per file rather than sliding smoothly.
Download each JPG from its own link, then use Process another to clear the tool before loading the next folder of bitmaps.

Three bytes per pixel and nothing else

The Windows bitmap is one of the simplest image formats ever standardised, and its simplicity is the whole story. A file header, an information header describing the dimensions and colour depth, an optional palette, and then the pixels, stored one after another with no compression applied. In the usual 24-bit form that means three bytes per pixel, blue then green then red, with each row padded out to a multiple of four bytes and the rows stored from the bottom of the image upwards.

That design made perfect sense when the format appeared. Decompression costs processor time, and the machines BMP was written for had very little of it; reading a bitmap into memory was close to a straight copy. What it means today is that file size is a direct function of pixel count, with no relationship to how complicated the picture is. A blank white rectangle and a detailed photograph of the same dimensions occupy exactly the same number of bytes.

JPEG attacks the problem from completely the opposite direction, spending processor time to store only what your eye is likely to notice. For the continuous-tone material people usually have sitting in bitmaps, scans, photographs and screenshots, that difference is the whole reason for converting.

Where BMP files still come from

Nobody chooses BMP on purpose any more, which is why finding one is usually a surprise. The common sources are all legacy paths that were never updated. Microsoft Paint used it as the default save format for many years, so older documents and tutorials are full of .bmp attachments. Plenty of flatbed and document scanners, particularly the ones bundled with all-in-one office printers, still offer bitmap as an output option and sometimes default to it.

Beyond that, it turns up wherever software was written once and left alone: laboratory and measurement instruments that export a screen capture, industrial control panels, medical and dental imaging front ends, point-of-sale terminals, older game asset pipelines and internal business tools written in the nineties. All of those emit bitmaps because writing a BMP takes about twenty lines of code and needs no library at all.

The problem is what happens next. Email systems reject the attachment on size, web forms and content systems refuse the extension or the size or both, chat apps take an age to send it, and a folder of scans fills a drive far faster than anyone expects. Converting to JPEG solves all of that at once.

No background fill on this converter

There is a difference between this page and PNG to JPG that is easy to miss. That tool paints the canvas with a background colour before drawing your image, because PNG genuinely carries transparency that JPEG cannot hold. This one does not, because bitmaps in real-world use are opaque; the module takes the plain conversion path deliberately, and the code says so.

For the overwhelming majority of files that is exactly right and saves a pointless step. The exception is the uncommon 32-bit BMP that really does carry an alpha channel, produced by some icon and game tooling. If you have one of those and the transparency matters, route it through a PNG first rather than straight to JPEG here.

Quality 90 against scans, screenshots and Paint drawings

The default of 90 is set higher than the presets on most of the other converters on this site, and the reason is the material. Bitmaps overwhelmingly hold scanned pages, screen captures and simple drawings, all of which are full of hard edges, and hard edges are precisely what JPEG’s block-based compression handles worst. Ringing around black lettering on white paper shows up at settings that would look flawless on a portrait.

So start at 90 and go up rather than down for a scanned document, especially if anyone will need to read the text or run it through recognition software later. Photographs scanned from prints behave like ordinary photographs and are comfortable well below the default. If the resulting JPGs are still larger than an upload form allows, Compress Image can take them further, and Image Converter covers the less common source formats that turn up alongside old bitmaps. The rest of the raster tools are collected on the image tools hub.

Convert BMP to JPG