PNG to BMP converter

Content last reviewed:2026-09-07

You upload PNG files and download finished BMP images. The converter writes 24 bits per pixel, value after value, so the file grows: our 1200 by 630 pixel screenshot went in at 139.2 KB and came out at 2.16 MB. All the work happens inside your browser.

Files in queue

Add PNG files on the left to start converting to BMP.

What is PNG and what is BMP?

PNG came about in 1995 for a specific reason: Unisys and CompuServe raised patent claims over the LZW compression that GIF rested on, and the web needed a format free of fees.[1] The group that designed it added the full range of colours along the way, as well as an alpha channel, which is a separate opacity value at every pixel. The description in force today is the third edition of the specification, published as a W3C Recommendation on 24 June 2025; it lists five image types, and two of them carry an alpha channel.[2]

BMP came earlier and from the opposite assumption. It is the simplest possible container for an image: a header with the dimensions, and after it the values of each pixel in turn. The format started in the OS/2 system, moved into Windows and stayed there for good.[3] That very simplicity is why people look for it today: a program that can only read bytes in order will display a bitmap without any library, because the pixels lie in it one straight after another.

Our converter writes one variant of the format: 24 bits per pixel, no compression, with a BITMAPINFOHEADER. That is the oldest and most widely read kind of BMP, so the finished file opens in every program that supports the format at all.

How do you convert PNG to BMP?

Drag your PNG files onto the Add files field, or click that field and pick the images from your disk. You can put many files into the queue at once. Then press the Convert button.

You download finished images one at a time with the Download button next to a queue row, or all together with the Download all button. The Clear all button empties the whole queue, and the Remove label next to a row takes a single file out of it.

In the queue on the right, every file shows its size before and after conversion together with the difference in per cent. Our 1200 by 630 pixel screenshot wrote Before: 139.2 KB · After: 2.16 MB (1492% more) there. The same summary for the whole batch sits under the buttons, in the Increased line.

The write itself is done by a BMP encoder written for this site and run on your own computer. The reason is simple: writing a bitmap straight from the canvas depends on the browser. We checked this on 6 September 2026: Firefox 153 returned a file starting with the letters BM, that is a real bitmap, while Chromium 151 returned a PNG file with the signature 89 50 4E 47. MDN documentation describes that behaviour plainly — with a format the browser does not know, you get a PNG and no warning.[4]

The file stays on your device from the first click to the end of the job. Under the converter sits a format switch reading PNG to BMP. Clicking either of the two formats opens a list, and picking from it takes you to the converter page for that pair. We have also gathered every pair from this group on the Format conversion subcategory page.

How much will the finished BMP file weigh?

You know that number before you upload anything, because it depends only on the dimensions of the image. Every pixel takes three bytes, every row is padded with zeros up to a full four bytes, and 54 bytes of header sit at the start of the file; Microsoft documentation gives a ready formula for this.[5]

Let us follow that through on an image measuring 1920 by 1080 pixels. One row holds 1920 pixels at three bytes each, which is 5,760 bytes. At this width nothing needs padding, because 5,760 divides by four. There are 1,080 rows, so the pixels alone take 6,220,800 bytes. Together with the header the file weighs 6,220,854 bytes, and it makes no difference whether it shows a photograph or one flat colour.

Padding matters at widths that do not divide by four. An image 1,001 pixels wide gives 3,003 bytes of data in a row, so the row is stretched to 3,004 bytes. Thanks to that single byte every row starts in the file at an address divisible by four, and a program reading the image can take the data four bytes at a time.

A PNG file works the other way round: its size cannot be predicted from the dimensions, because it depends on what the picture shows. That is why the growth here is sometimes twofold and sometimes fiftyfold — what decides it is how well the content of the image packed down beforehand. The opposite direction is handled by the BMP to PNG converter.

How much does the same image weigh in PNG and in BMP?

We put five images of different kinds through this converter. We give the sizes exactly as the tool counts them: in kilobytes and megabytes of 1024, with the same rounding.

Image	Size in pixels	PNG	BMP	How many times larger
Camera photo	3000 × 2000	13.1 MB	17.2 MB	1.3
Photo for a website	1280 × 850	1.96 MB	3.11 MB	1.6
Scan of a book page	1200 × 1600	1.98 MB	5.49 MB	2.8
Screenshot of an interface	1200 × 630	139.2 KB	2.16 MB	15.9
Graphic made of flat areas	800 × 600	28.9 KB	1.37 MB	48.7

Our own measurement from 6 September 2026, taken in a browser built on the Chromium engine, version 151. All five dropped into the queue at once gave 17.2 MB on the way in and a line reading Increased: 12.1 MB (~70% more). The BMP column does not depend on the content of the image, so the same dimensions will give you the same numbers. Only the PNG column changes, and it is what decides how many times the file grows.

What happens to transparency?

A 24-bit write gives all three bytes of a pixel to colour. The converter therefore lays the image over a white background before it reads the pixels. We prepared an 800 by 600 pixel test file with three levels of opacity and checked each of them separately.

Pixel opacity in the PNG file	How many such pixels the file held	Colour in the PNG file	Colour in the finished BMP
Full, value 255	210,000	219, 38, 38	219, 38, 38
Half, value 128	60,000	219, 38, 38	237, 146, 146
None, value 0	210,000	219, 38, 38	255, 255, 255

Our own measurement from 6 September 2026. A fully opaque pixel comes out of the converter with values identical down to the unit to those it went in with. A pixel at opacity 128, that is half transparent, is mixed with white in equal parts: 219 and 255 give 237, while 38 and 255 give 146. A fully transparent pixel takes on plain white. The same arithmetic repeated in Firefox 153, so the result does not depend on the browser.

What is the difference between PNG and BMP?

Format feature	PNG	BMP
Compression	Lossless: row filtering, then Deflate	None in the variant this converter writes
Size of a 1920 × 1080 image	Depends on the content of the image	Always 6,220,854 bytes
Transparency	Alpha channel in two of the five image types	Transparent areas get a white background
Colour depth	from 1 to 64 bits per pixel, depending on the image type	24 bits per pixel in this write
Row order inside the file	from the top row down	from the bottom row up
Written straight from a browser canvas	The default format, every browser	Firefox yes, Chromium no
Origin	The PNG working group, 1995	The OS/2 system; it reached Windows in 1990 with version 3.0

What PNG can do is taken from the third edition of its specification[2] and the encyclopedia entry on that format[1], and what BMP can do from Microsoft documentation[5] and the entry on that format[3]. The row about writing from a canvas is our own measurement from 6 September 2026 in Chromium 151 and Firefox 153. Both formats are read by every browser, which the MDN guide lists.[6]

What does the converter do with a PNG file?

Eight things worth knowing before you drop a larger batch of images into the queue.

It writes a single kind of BMP, the most widely read one
The finished file has 24 bits per pixel, a BITMAPINFOHEADER 40 bytes long and no compression. Firefox writes the same variant in its own canvas encoder, which we checked on the same images: its file and ours came out the same length down to the byte.
The pixel count stays the same
A 3000 by 2000 pixel photo comes out as a BMP measuring 3000 by 2000 pixels. Only the way of writing changes, while the frame and the resolution stay untouched.
The colour of opaque pixels stays unchanged
We compared the pixel values before conversion and after it. On the 3000 by 2000 pixel photo all 6,000,000 pixels were fully opaque, and all of them came out with the same colour, down to the unit.
It lays transparent areas over white
The converter fills the canvas with white before it puts the image on it. A cut-out background therefore comes out white rather than black — a pixel with no colour and no opacity, written straight through, would give black.
The result is written in full colour
Three bytes per pixel give 16.7 million shades, the same range PNG carries at eight bits per channel. We write the components in the order blue, green, red, because that is how a row looks inside a BMP file.
A single file up to 100 MB
That is what the converter takes from one PNG file. With a larger one it shows the message File is too large (max 100 MB). The limit applies to the input file, and the finished BMP may come out considerably heavier.
Very large images are fitted to the canvas
A browser canvas holds 16,384 pixels per side and around 268 million pixels in total. The tool scales an image beyond that limit proportionally. At the limit itself the finished bitmap weighs 768 MB, so it is worth having room for it on disk.
The write takes a fraction of a second
The encoder runs on your own computer, so the time depends on its power. All five images, weighing 17.2 MB together, went through our queue in 1.2 seconds, and the bar above the buttons shows how many files are already done.

When should you pick BMP, and when another format?

A program or device reads bitmaps only
Display drivers, older industrial applications and embedded systems often take BMP alone, because reading such a file means copying bytes into memory. This is the situation where BMP is simply the right format.
You are writing code that reads pixels itself
A bitmap lets you get at a pixel value with no library at all: you work out the offset from the start of the data and read three bytes. When learning raster graphics, and in small home-made tools, that saves the whole decoding stage.
The image has to keep a transparent background
Then the file stays in a format that carries an alpha channel. A logo with the background cut away and an interface icon keep their shape in PNG, and a lighter file with the same transparency comes from the PNG to WebP converter or the PNG to AVIF converter.
The image goes onto a website
The MDN guide advises plainly against using BMP for website content, and gives the size of an uncompressed file as the reason.[6] What suits the web is a file that weighs a dozen or so times less at the same quality — the PNG to WebP converter will prepare one.
A photo goes by email or onto a shared drive
A photograph in a bitmap takes a dozen or so megabytes every time. When the file has to be light and small colour differences do not matter, the PNG to JPG converter is the handier choice.
The other direction
You can pack a finished bitmap back losslessly with the BMP to PNG converter. The same image in a smaller file still comes from the BMP to WebP converter.

Convert other files to BMP

AVIF to BMP JPG to BMP WebP to BMP TIFF to BMP

Convert PNG to other formats

PNG to JPG PNG to WebP PNG to AVIF PNG to GIF PNG to TIFF PNG to PDF PNG to Base64

Sources

PNG — Wikipedia
Portable Network Graphics (PNG) Specification, Third Edition — W3C
BMP file format — Wikipedia
HTMLCanvasElement: toBlob() method — MDN Web Docs
Bitmap Storage — Microsoft Learn
Image file type and format guide — MDN Web Docs

The file sizes in the tables were measured by running finished images through this converter in a browser, and we report them the way the tool counts them. What the page says about either format rests on the sources listed above.

Content last reviewed: September 7, 2026 · written and checked by the Arteon team

Common questions about turning PNG into BMP

Why is the file larger after conversion?

Because BMP in this variant writes every pixel separately and in full, with no packing at all. PNG does the opposite: it predicts a pixel value from its neighbours, stores only the difference, and then packs the result with Deflate compression. The better an image packed down beforehand, the more it grows after conversion. In our measurement the camera photo grew 1.3 times. The graphic made of flat areas, which packs down best of all, grew 48.7 times.

Exactly how much will my file weigh?

As much as follows from the dimensions of the image. Multiply the width by three, round up to a full four bytes, multiply by the height and add 54 bytes of header. For an image 1920 by 1080 pixels that gives 6,220,854 bytes. The content of the image does not change that number by a single byte.

Will I lose quality converting PNG to BMP?

Opaque pixels come through unchanged — on the 3000 by 2000 pixel photo we checked all 6,000,000 of them and every one came out with the same colour. What changes are only the areas that were transparent in the PNG file, because a 24-bit write gives all three bytes of a pixel to colour and those areas land on a white background.

What exactly happens to a transparent background?

The converter paints a white background and only then lays the image on it. A fully transparent pixel takes on pure white. A half-transparent pixel mixes with white in proportion to its opacity: our red at values 219, 38, 38 with opacity 128 came out as 237, 146, 146. When the background has to stay cut out, the file needs to remain in a format with an alpha channel.

Why does the converter have its own BMP encoder?

Because writing this format from a canvas depends on the browser. We checked it on 6 September 2026 on the same images: Firefox 153 returned a real bitmap starting with the letters BM, while Chromium 151 returned a PNG file with the signature 89 50 4E 47, even though the request was for BMP. MDN documentation describes that behaviour plainly.[4] Our own encoder gives the same result in every browser.

Do my files reach a server?

No. The image is loaded by the page code in your browser, drawn onto a canvas (Canvas API) and passed from there to the encoder, which also runs locally. The file stays on your device for the whole job and disappears from the browser's memory once the tab is closed.

Which kind of BMP will I get on output?

A 24-bit write with a BITMAPINFOHEADER, no compression, rows laid out from the bottom up and components in the order blue, green, red. We also write a resolution of 96 dots per inch into the header. That is the oldest variant of the format, so every program that supports BMP at all will open it.

How many files can I convert at once?

You can add as many files to the queue as you like, and the tool works through them one after another and shows the progress above the buttons. Five images weighing 17.2 MB in total went through our queue in 1.2 seconds. A single input file may weigh up to 100 MB, and the total number of files depends on the memory of your device.