Why Is Your File Bigger Than Expected? Common Causes and Fixes
You compressed the file. It's still too big. Here's what's actually happening, ranked from most to least common.
1. You Compressed the Wrong Format
PNG files resist compression far more than JPG for photographic content — if you're starting from a PNG photo and struggling to hit a small KB target, converting to JPG first (even before adjusting quality) often solves the problem immediately. See our format comparison guide for when each format makes sense.
Fix: Switch the output format to JPG before compressing further.
2. The Resolution Is Higher Than It Needs to Be
A 4000×3000 pixel photo carries far more data than a form actually displays — compressing quality alone without reducing dimensions leaves you fighting an uphill battle. Reducing resolution first (via Resize by Pixels in Advanced Settings) often gets you to a small target size with better visible quality than quality-compression alone.
Fix: Set a Max Width/Height before compressing, especially for photos taken on modern phone cameras (often 12+ megapixels).
3. You're Compressing an Already-Compressed File
Re-compressing a JPG that's already been compressed once yields diminishing returns — much of the "easy" size reduction already happened. If possible, always start from the original, uncompressed source file.
Fix: Locate the original photo (not a screenshot or a previously-downloaded compressed copy) and compress that instead.
4. Your PDF Has Many High-Resolution Scanned Pages
Each scanned page in a PDF is effectively a full embedded image — a 10-page scanned document can easily be 20-30 MB before compression. There's a practical floor to how small this can get while staying legible.
Fix: Try Grayscale mode if the original is black-and-white, or consider whether all pages are actually needed in one file.
5. Your Counting Standards Are Off
A file that measures 205 KB on your computer might read differently on another system due to binary vs. decimal counting conventions — see our full MB vs KB explainer for the details. This rarely explains a large gap, but can explain a small one right at a size limit's edge.
Fix: Always check the live compressed size shown by your tool, not a manually calculated estimate.
Frequently Asked Questions
I compressed to "Maximum" and it's still too big — what now?
Check the format first (PNG resists compression more than JPG), then check resolution — extremely high-resolution originals may need resizing, not just quality reduction, to hit small targets.
Why does the same photo compress differently on different tools?
Different compression algorithms and settings prioritize different tradeoffs — some prioritize speed, others maximum size reduction, others visual fidelity. Small differences in output size between tools are normal.