Is PNG always bigger than JPG?

No, that is a common misconception. PNG is only bigger than JPG on photographic content, because the continuous colour variation in photographs does not suit PNG's lossless compression method. By contrast, PNG frequently comes out smaller than JPG for screenshots, interface captures, logos, diagrams and graphics containing flat colour areas. So the type of content directly determines the size outcome; there is no rule of thumb.

Which should I choose if I'm not sure?

If you are not sure, choose PNG. PNG is lossless, meaning it preserves your BMP's pixels one-to-one, so there is no price to pay for deciding wrongly. You can change your mind later and produce a JPG from the PNG while still holding a full-quality copy. In the other direction you have no such luck: if you produce a PNG from a JPG, the discarded data does not come back and you have merely put a degraded image into a lossless container. When in doubt, choosing the reversible option is always right.

Can I just produce both?

You can, and in many cases it is the most sensible approach. Keep the PNG as your storage and editing copy, and produce the JPG for sharing and web use. That way you have both a full-quality lossless copy and a file that is easy to send. Once you have produced both, you can comfortably delete the original BMP, because the PNG holds all the pixel information it carried in far less space.

Which should I choose if the BMP has transparency?

PNG, without hesitation. JPG does not support transparency at all; when you convert an image carrying an alpha channel to JPG, transparent areas are filled with a solid colour, usually white or black, and that cannot be undone. Since alpha support in BMP is inconsistent to begin with, it is worth checking first whether the image really does carry transparent regions. If it does and they need to be preserved, PNG is the only valid target.

BMP to JPG or PNG? Which Should You Convert To?

The same file, two different routes

You have a BMP and you need to make it smaller. Two sensible targets present themselves: JPG and PNG. Online, the two are usually summarised as "JPG is small, PNG is high quality", but that summary is crude enough to lead you to the wrong decision on a BMP conversion.

The right answer depends on a single question: what is inside your BMP file?

In this article we answer that question with concrete examples and compare what each route actually gains and costs you.

The two conversions are entirely different in nature

Let's establish the mechanical difference first, because the rest of the comparison rests on it.

BMP → PNG is a lossless-to-lossless transition. Both formats store pixel values exactly. The difference is that PNG compresses those values intelligently: it spots repeating patterns and similarities between neighbouring pixels and saves space. The result is an identical image in a far smaller file. You lose nothing.

BMP → JPG is a lossless-to-lossy transition. JPG calculates and discards the information the human eye barely notices. The file comes out even smaller than PNG, but the discarded data does not come back. This operation is one-way.

So PNG carries no price and JPG does. Whether the price is worth paying depends on the content.

The decision table by content

Photographs and photograph-like content

Natural texture, smooth colour gradients, shadows, skin tones — in short, anything that looks like it came out of a camera.

Winner: JPG. This content is what JPG was designed for. Its compression algorithm works extremely efficiently on continuous colour variation and, at reasonable quality settings, shrinks the file considerably without leaving visible loss. The PNG version of the same photograph will be noticeably bigger, and in return for that bulk you gain no practically perceptible quality.

Screenshots, interface captures, text

Menus, buttons, tables, software windows, scanned pages of text.

Winner: PNG, by a distance. JPG loses on two fronts here. First quality: JPG compression produces grey shadowing around sharp letter edges — known as ringing — and blurs fine interface lines. The result is legible but looks dirty. Second size: screenshots consist of large flat colour areas and PNG compresses those extremely efficiently. So for this content PNG is usually both cleaner and smaller. Converting the BMP to PNG is unarguably the right call in this scenario.

Logos, icons, drawings, diagrams

A small number of flat colours, sharp edges, crisp contours.

Winner: PNG. The same logic as screenshots applies here, only more strongly. Flat colour areas are ideal for PNG; JPG leaves visible blurring around sharp contours. Storing a logo as JPG means using a degraded copy every time you use it.

Images containing transparency

Winner: PNG, no alternative. JPG does not support the alpha channel. Transparent areas are filled with a solid colour and it cannot be undone. Since BMP's alpha support is inconsistent to begin with, check first whether your file really contains transparent regions — but if it does, the decision is obvious.

Images that will be edited later

Winner: PNG. JPG's loss is cumulative: every time you open and save, compression is reapplied and degradation accumulates. Keeping the file you will work on lossless prevents quality from quietly eroding during editing.

If you cannot decide

There is a practical rule: when in doubt, choose PNG.

The reason is simple. Because PNG is lossless, there is no price for deciding wrongly. If you later think "actually JPG would have been better", you can produce a JPG from the PNG and the full-quality copy remains in your hands. The other direction is irreversible — producing a PNG from a JPG does not bring back the discarded data, it merely puts a degraded image into a lossless container.

In many cases the most efficient approach is to produce both: PNG as the storage copy, JPG as the sharing copy. Once those two are ready, you can delete the original BMP with a clear conscience, because the PNG carries all of its pixel information in far less space.

The thing neither option offers

One final note of honesty: neither of these two routes improves your image.

Because BMP is uncompressed, it stores whatever quality it holds. If the file is blurry, low-resolution or already degraded at the source, PNG will preserve that degradation losslessly, while JPG will add a little more loss on top. The format choice determines size and storage behaviour; not the image itself.

In summary

JPG for photographs, PNG for everything else. If there is transparency, PNG. If editing is coming, PNG. If you are not sure, PNG. Use JPG as a deliberate choice, on photographic content where you genuinely need the smallest possible file — and knowing that the file you produce is now its final form.