Convert a BMP to PNG on Mac

Someone sent you a .bmp file and you opened it expecting a tiny graphic — instead it’s 12 MB for a 1000-pixel image. BMP is an old uncompressed format that’s still hanging around in legacy Windows workflows. PNG gives you the same lossless quality at roughly a tenth of the size.

Why convert

• BMP is uncompressed. A 2000×2000 BMP is around 12 MB; the same image as PNG is usually 1–2 MB.
• BMP doesn’t compress well even with zip. PNG’s internal compression is already doing that work.
• Web tools and modern design apps prefer PNG. Some don’t accept BMP at all.

The native way: Preview

Preview opens BMP and exports to PNG cleanly:

1. Open the BMP in Preview.
2. File → Export.
3. Choose PNG.
4. Save.

Fine for a single file.

The native way: sips

For batches:

sips -s format png image.bmp --out image.png

A folder of BMPs:

for f in *.bmp *.BMP; do
  sips -s format png "$f" --out "${f%.*}.png"
done

Both methods are lossless — you don’t lose any image data going from BMP to PNG.

The faster way

Drop the folder into Melt, set output to PNG, click Compress. Handy when you’ve got dozens of legacy BMPs to bring into a modern workflow. Download Melt.

Bulk convert in Melt

1. Open Melt.
2. Drag your BMP files or folder in.
3. Set output to PNG.
4. Click Compress.

When you’d convert to JPEG instead

If the BMPs are actually photographs (rare but it happens with old screenshots of camera output), JPEG at quality 85 will be even smaller than PNG. For anything with text, sharp edges, or transparency — screenshots, diagrams, UI captures — stick with PNG.

sips -s format jpeg -s formatOptions 85 image.bmp --out image.jpg

What you lose, what you keep

PNG conversion from BMP is lossless — the image bytes are identical pixel-for-pixel, just compressed. You don’t lose colour depth, you don’t lose sharpness, you don’t lose anything except disk space. BMPs rarely have meaningful metadata, so there’s nothing else to worry about losing.

If you only need the PNG copies going forward, archive the BMPs somewhere (or just delete them — they’re recreatable from the PNGs at no loss). Storage savings are usually 80–90% per file.