How to Convert BMP to PNG — Same Pixels, Much Smaller File (2026)

1. Quick Answer

2. Why Convert: Uncompressed vs Lossless-Compressed

The entire case for this conversion comes down to one fact: BMP stores pixels raw, PNG stores the same pixels compressed — and the compression is lossless.

A standard 24-bit BMP allocates exactly 3 bytes for every pixel, no matter what the image looks like. The arithmetic is brutal: a 1920×1080 screenshot is 1920 × 1080 × 3 ≈ 6.2 MB, every single time. A 3840×2160 (4K) image is about 24.9 MB. A white rectangle costs as much as a detailed photograph. (BMP does define an optional RLE compression mode, but almost no software uses it — real-world BMPs are effectively always uncompressed.)

PNG, standardized in 1996, compresses pixel data with DEFLATE — the same lossless algorithm ZIP files use — plus pixel-prediction filters that make image data compress far better than naive zipping. Lossless means exactly that: when the PNG is decoded, you get back every pixel value bit-for-bit identical to the source. Nothing is estimated, approximated, or thrown away — which is the crucial difference from JPG, where compression permanently discards detail.

How much smaller, realistically?

• Screenshots, UI captures, diagrams, charts, scans of text — large flat-color areas compress superbly: typically 80–95% smaller. A 6.2 MB BMP screenshot commonly becomes a 200–600 KB PNG.
• Photographs and noisy images — less redundancy to exploit, but still meaningful: typically 30–60% smaller.
• Worst case — pure random noise barely compresses, but even then PNG will not be larger by more than a rounding error, and real images are never pure noise.

Since BMPs most often come from screenshot tools, scanners, and legacy Windows software — exactly the flat-color-heavy content PNG compresses best — the typical user sees the dramatic end of that range.

3. BMP vs PNG — Side by Side

4. Method 1: Convertlo Browser Converter (Any Device, Batch)

Convertlo's converter runs entirely in your browser — the BMP is decoded and re-encoded as PNG locally on your device, so nothing is uploaded to any server. It also handles multiple files at once, which Paint and Preview cannot do without manual repetition.

5. Method 2: Microsoft Paint (Windows, Built-In)

Every Windows machine since 1985 ships with Paint, and Paint reads BMP natively — it is the format's home turf. For a single file this takes seconds:

1. Right-click the BMP file and choose Open with → Paint
2. Click File → Save as → PNG picture
3. Choose a location and click Save

The Windows Photos app works too: open the BMP, click the three-dot menu, choose Save as, and pick PNG as the file type. Both methods are free and offline. The limitation of both: strictly one file at a time. If a scanner or legacy application has left you a folder of dozens of BMPs, use the browser batch method above instead of repeating the Paint dance per file.

6. Method 3: Mac Preview (Built-In)

macOS opens BMP files in Preview out of the box, and Preview exports to PNG directly:

1. Double-click the BMP — it opens in Preview
2. Click File → Export…
3. In the Format dropdown, choose PNG, then click Save

For several files, Preview has a semi-batch trick: select all the BMPs in Finder, open them together in one Preview window, select all thumbnails in the sidebar (Cmd+A), then use File → Export Selected Images… and choose PNG as the format. Finder's Quick Actions → Convert Image also offers PNG output on modern macOS versions.

7. When NOT to Convert BMP to PNG

Honesty section — two cases where this conversion is the wrong move:

• The file must go back into a BMP-only system. Some legacy industrial, medical, and point-of-sale software reads only BMP. Keep the original BMP for that system and convert a copy for everything else.
• You actually want the smallest possible file and do not need lossless. For photographs destined for email or the web, a high-quality JPG is several times smaller than even a PNG. See our BMP to JPG guide for that path — the trade-off is that JPG is lossy, so it is wrong for screenshots with text and for anything you may edit again.

8. Frequently Asked Questions