Tool
Compress Image
Shrink image file size to a target limit, with the quality tradeoff shown.
Real compression results, not estimates
Every number on this page came from actually uploading a file to ConvertBrio's live compressor and measuring what came back, the same endpoint your browser calls when you use the tool above. Nothing here is simulated.
Methodology
The test file is a 2000 × 1500, 814.8 KB synthetic JPEG we generated ourselves: a soft gradient portrait composition with photographic-grain noise layered on top, built to compress like a real phone photo without using anyone's actual photo (for privacy) or a downloaded stock image (for licensing). We ran it through /api/convert/image with each target size below and recorded the exact response. Tested in Chrome on macOS: conversion runs entirely on ConvertBrio's servers, so the result is identical regardless of which browser or device sends the request.
Before / after at each target size
Measured results
| Target | Achieved | Dimensions | Compression ratio | Hit target? |
|---|---|---|---|---|
| 200 KB | 199.7 KB (204,495 bytes) | 2000 × 1500 (unchanged) | 4.1× smaller | Yes |
| 100 KB | 99.2 KB (101,640 bytes) | 2000 × 1500 (unchanged) | 8.2× smaller | Yes |
| 50 KB | 48.1 KB (49,314 bytes) | 2000 × 1500 (unchanged) | 16.9× smaller | Yes |
| 20 KB | 14.9 KB (15,357 bytes) | 1700 × 1275 (−15% width) | 54.3× smaller | Yes |
The 200–50 KB targets were all hit on quality reduction alone, at full original resolution. The 20 KB target needed one downscale step (2000px → 1700px wide, −15%) because quality reduction alone couldn't fit that far below the original: visible detail loss starts to show at this level; see limitations below.
Format matters: JPEG vs. PNG at the same target
We ran the identical test image through the same 100 KB target twice: once saved as JPEG, once as a lossless PNG re-encode of the same pixels (6.35 MB original). JPEG hit the target at full 2000×1500 resolution. PNG needed to drop to 887×665 (44% of the original width) and fall back to 256-color palette quantization, which introduces visible dithering speckle. If your source format is flexible, JPEG or WEBP will preserve more detail at the same target size than PNG.
Supported format matrix
| Input format | Output format | Notes |
|---|---|---|
| JPEG | JPEG | N/A |
| PNG | PNG | Uses palette quantization to hit small targets: see limitations below |
| WEBP | WEBP | N/A |
| AVIF | AVIF | N/A |
| GIF | GIF | Only the first frame is kept: animation isn't preserved |
| HEIC / HEIF | JPEG | HEIC/HEIF aren't supported output formats, so iPhone photos convert to JPEG |
How target-size compression actually works
Processing runs server-side using sharp (built on libvips). When you set a target size, ConvertBrio binary-searches JPEG/WEBP/AVIF quality between 10% and 95%, re-encoding and measuring the actual output at each step, until it finds the highest quality that still fits your target, typically in 6–7 attempts. PNG targets add palette quantization to that same search, since plain PNG quality settings barely change file size on their own. If the target still can't be hit at the 10% quality floor, the tool falls back to shrinking the image's dimensions by 15% at a time (up to 6 steps) and retries, rather than pushing quality below a usable threshold.
Limitations and edge cases
- Very aggressive targets relative to the source (well under the 20 KB case tested above) can require dropping dimensions to a fraction of the original before the file fits: there's a real quality floor, not just a size floor.
- PNG compresses far less efficiently than JPEG/WEBP for photographic content (see the format comparison above) because it relies on palette quantization rather than true lossy encoding.
- Animated GIFs are compressed as a single still frame: we tested this directly with a 3-frame GIF and confirmed the output keeps only the first frame.
- HEIC/HEIF photos (the default format on recent iPhones) always come back as JPEG, since HEIC isn't a supported output format: expect a different file extension than what you uploaded.
- Uploads are capped at 100 MB on the free tier.
Image Compressor: Shrink Images to a Size Limit, With Quality Tradeoffs Explained
Whether you're hitting an upload limit, speeding up a website, or just tired of photos eating up storage, ConvertBrio's image compressor reduces file size at a quality cost you can see and control. Set a quality level, or give the tool a maximum size in kilobytes (1 KB = 1,024 bytes) and it searches for the best quality that lands at or below that ceiling.
That target-size mode is the reason most people land here. Visa portals, job sites, university applications, and government forms routinely cap a photo or document scan at 100 KB, 200 KB, or 50 KB, and rejecting a 4 MB phone photo with no guidance on how to shrink it. Instead of exporting at guessed quality levels until one happens to fit, you type the limit once and download a file that's under it.
How to use this tool
- 1
Upload the image
Drag in a JPG, PNG, WEBP, HEIC, or AVIF file, up to 100 MB. HEIC photos from an iPhone are accepted directly.
- 2
Set a target size, or a quality level
Enter the maximum file size you need in KB (for example 100). Leave it blank to use the quality slider instead, where lower values mean smaller files.
- 3
Compress
ConvertBrio re-encodes the image, and in target mode it adjusts quality, then dimensions if quality alone isn't enough, until the file fits under your limit.
- 4
Download the result
The compressed file downloads automatically. Check it looks acceptable; if it's too soft, raise the target or quality and run it again.
How image compression works
JPG, WEBP, and AVIF are lossy formats: they shrink a file by discarding image data the human eye is least likely to miss: subtle colour gradients, fine texture in busy areas, high-frequency detail. Lowering the quality setting tells the encoder to discard more, which produces a smaller file with progressively more visible softening and blocky artifacts.
PNG is lossless and compresses differently: it can only pack the exact pixels more efficiently, so a photo saved as PNG barely shrinks. If you upload a PNG photo to the compressor and want a real size reduction, converting it to JPG or WEBP first (with the Image Converter) will do far more than any PNG compression can.
Reducing an image to a size limit (like 100 KB)
Enter your limit in the target-size field and ConvertBrio works backward to it: it searches for a quality setting (a binary search, re-checking the encoded size each time), and only if the smallest reasonable quality still overshoots does it reduce the pixel dimensions as well. The result is the best-looking version it found that fits at or under the ceiling, so a 100 KB limit may produce, say, a 99 KB file rather than exactly 100 KB. If even the lowest quality doesn't fit, you'll see the smallest size it reached.
- Passport / visa photo uploads: often 100 KB or a 10 KB–240 KB range
- Government and tax portals: commonly 100 KB or 200 KB per document scan
- Job application sites: frequently 50 KB–500 KB for a CV photo or certificate
- Forum and marketplace avatars: often capped near 1–2 MB
How much can you compress before it shows?
Most photographs can lose 40–60% of their file size with no difference visible at normal viewing size, because the first data an encoder discards is genuinely hard to see. Past that point, flat areas like skies start to band, and edges around text or fine detail get crunchy. The practical method is to start near the top of the quality range and step down while watching the image, rather than jumping straight to a low number.
Compressing vs resizing
Compression keeps the same pixel dimensions and reduces how much data each pixel costs. Resizing reduces the pixel count itself. For a photo that's both physically huge (6000 px wide) and heavy, resizing to the dimensions you actually need, then compressing, gets you a much smaller file than compression alone, with less visible quality loss. Use the Resize Image tool for that first step.
Privacy and limits
Every upload is encrypted in transit and automatically deleted from ConvertBrio's servers within about 24 hours, downloaded or not. This tool compresses one image per upload, up to 100 MB, free, with no account and no watermark.
Related Tools
Compress Image: FAQ
Common questions about compressing and reducing image file size.
How do I reduce an image to under 100 KB?
Upload the image to ConvertBrio's compressor and set the target size to 100 KB. The tool lowers quality, and dimensions if needed, until the file fits that limit, which is ideal for forms and ID uploads with strict size caps.
Will compressing my image make it look worse?
At moderate compression, most people can't tell the difference. Quality loss becomes noticeable only at aggressive settings, so it's worth checking the result rather than compressing to the smallest possible size by default. If a strict target forces heavy compression, resizing the image smaller first will help it look better at the same file size.
My PNG barely got smaller, why?
PNG is lossless, so there's little room to compress a photograph stored in it. Convert the PNG to JPG or WEBP with the Image Converter first; that alone often cuts the size by 70% or more.
Does the compressor keep the image's dimensions?
Yes, unless you use target-size mode and the file still won't fit after maximum quality reduction, in that case it also scales the dimensions down as a last resort to meet your limit.
Can I compress multiple images at once?
Compressing one image per upload is free with no account required. This tool doesn't currently batch-process multiple images in a single pass.
What formats can I compress?
JPG, PNG, WEBP, HEIC/HEIF, and AVIF. The output is returned in a web-friendly format suited to the smallest size at your chosen quality.