Image File Size Estimator
Encode the same image at several qualities and in several formats in the browser, and compare the resulting sizes to find the point where further quality costs bytes without visible gain.
Last reviewed by the Radiatus Cloud team
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The quality slider is not linear
Moving JPEG quality from 95 to 85 typically removes half the file size and produces a difference almost nobody can see. Moving from 85 to 75 removes far less and starts to show. The relationship between quality and size is steep at the top and flat at the bottom, which means the highest settings cost an enormous number of bytes for almost no visible benefit. Finding where the curve flattens for a particular image is the entire exercise.
Format matters more than quality
WebP typically produces files 25 to 35 percent smaller than JPEG at visually equivalent quality, and AVIF smaller still, often by half. Switching format usually saves more than any amount of quality tuning within a format, and it costs nothing in compatibility now that both are supported everywhere that matters. Measuring rather than assuming is what this does, because the advantage varies considerably with the content.
Different content compresses differently
A photograph with smooth gradients compresses well in JPEG and poorly in PNG. A flat illustration is the opposite: PNG stores it compactly and losslessly while JPEG both enlarges it and introduces artefacts around every edge. Screenshots containing text are the clearest case, where PNG is often smaller as well as sharper. Encoding the actual image is the only reliable way to know, since the general rules have many exceptions.
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Frequently Asked Questions
What JPEG quality should I use?
Usually between 75 and 85. Above 85 the file grows quickly for differences almost nobody can see, and below 75 artefacts start to appear around edges. The exact point where the curve flattens varies by image, which is what measuring shows.
Is WebP always smaller than JPEG?
Usually, by 25 to 35 percent at equivalent quality, and not always. For some images with heavy fine detail the advantage narrows. Measuring the actual file is the only way to be sure for a particular image.
When is PNG the right choice?
For flat illustrations, logos, screenshots containing text, and anything needing transparency. PNG is lossless, so it does not introduce the artefacts JPEG creates around every sharp edge, and for such images it is frequently smaller too.
Why is my PNG so large?
Because PNG is lossless and photographs contain far too much varied detail to compress well that way. A photograph as PNG is typically several times larger than a visually identical JPEG.
Are these sizes exact?
They are what your browser encoder produces, which is close to but not identical to what a build tool would. Encoders differ in their settings and optimisation passes, so treat the comparison between formats as reliable and the absolute numbers as approximate.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Upload an image to see its encoded size across formats and quality settings.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
Related Tools
EXIF Viewer
ImageExtract hidden EXIF data (Camera, GPS, Settings) from images.
Favicon Generator
ImageGenerate favicons and app icons at every required size from one source image, with the exact HTML to reference them.
Placeholder Image Generator
ImageGenerate placeholder images at any size with custom colours and label text. Produced in your browser as downloadable files, no external hotlinking.