How to Compress PNG to a Specific File Size

One of the most specific image challenges people face is the requirement to compress PNG to a specific size. Job application portals, government forms, school systems, and many web platforms specify maximum file sizes like "profile photo must be under 100 KB" or "document scan must be under 500 KB."

The challenge with PNG is that it's a lossless format — there's no quality slider you can turn down to reduce size. Instead, the main levers are dimensions (width and height) and format.

Why you can't directly set a PNG output file size

Unlike JPG where you can set a quality level and somewhat predict output size, PNG size is determined by the image content. A PNG with many unique colors will be larger than one with flat blocks of color, at the same dimensions. This makes it impossible to set "save as PNG, 100 KB" directly.

The practical solution: reduce dimensions and optionally switch to JPG or WebP to hit the target.

Strategy to compress PNG to 100KB or less

• Start with dimensions. If you need the output under 100 KB:
  • A 400 × 400 px photograph as JPG (85% quality): ~30–60 KB
  • A 600 × 600 px photograph as JPG (85% quality): ~60–120 KB
  • A 800 × 600 px photograph as WebP: ~50–100 KB
• Use JPG or WebP instead of PNG for photographs. Photographs compress extremely well with JPG and WebP. If the requirement just says "image under 100 KB" without specifying PNG, using JPG or WebP is the easiest path.
• Iterate: Start with estimated dimensions, check the output size, and adjust. With Resizo, you can quickly try different dimension combinations.

Step-by-step: compress PNG to specific size with Resizo

• Step 1: Open Resizo and load your PNG.
• Step 2: Estimate starting dimensions. For under 100 KB in JPG, try 500 × 500 px as a starting point for a typical photograph.
• Step 3: Select JPG or WebP as output format for better compression than PNG.
• Step 4: Download and check the file size. If it's still too large, reduce dimensions further and try again.
• Step 5: If you must keep PNG format, reduce dimensions significantly — a 300 × 300 px PNG photograph is typically 100–300 KB depending on content.

Typical size targets and what dimensions achieve them

• Under 50 KB: 300 × 300 px JPG, or 400 × 400 px WebP
• Under 100 KB: 500 × 500 px JPG, or 700 × 700 px WebP
• Under 200 KB: 800 × 600 px JPG, or 1000 × 800 px WebP
• Under 500 KB: 1200 × 900 px JPG, or 1600 × 1200 px WebP

These are rough guidelines. Actual sizes vary based on image complexity (a photo of a forest with millions of detail variations will be larger than a photo of a white wall at the same dimensions).

When the system specifically requires PNG

If a form specifically requires PNG and under 100 KB, you will need to reduce dimensions significantly. For a photograph, you're looking at 300 × 300 px or smaller. For a logo or graphic with flat colors (which PNG compresses much better), you can achieve under 100 KB at larger dimensions like 600 × 600 px.