Image File Size Estimator (JPEG vs PNG vs WebP)

Four very different file sizes for the same 1920x1080 image

A 1920x1080 image at 24-bit color depth has an uncompressed raw size of 6,220,800 bytes (about 5.9 MB). Compressed, that same image is estimated at roughly 414,720 bytes as JPEG (quality 80), 290,304 bytes as WebP, and 3,110,400 bytes as PNG.

The gap between raw and JPEG here (6.2 MB down to about 405 KB, a 15x reduction) illustrates why lossy compression exists at all -- JPEG discards visual information a viewer is unlikely to notice, achieving dramatically smaller files at the cost of some image fidelity, unlike PNG's lossless compression, which preserves every pixel exactly and therefore can't shrink the file nearly as much.

WebP estimating smaller than JPEG at a comparable quality level (290 KB vs. 415 KB here) reflects WebP's generally more efficient compression algorithm -- a big part of why WebP has become a popular JPEG replacement for web images where smaller file sizes directly improve page load speed.

Why these are estimates, not guaranteed exact sizes

Heuristics only: JPEG ~ raw * (quality/100) / 12, WebP ~ JPEG * 0.7, PNG ~ raw * 0.5. Not an encoder. This tool uses simplified heuristic formulas, not an actual image encoder -- real compressed file size depends heavily on the specific image content itself (a photo of a complex, detailed scene compresses differently than a simple graphic with large flat color areas), which these generic formulas can't account for.

PNG's estimate here (raw x 0.5) is a rough approximation for typical photographic content -- PNG's actual compression ratio varies enormously by image type, performing much better on images with large flat color areas or limited color palettes (like screenshots or logos) than on complex photographic detail.

JPEG quality (80 here) directly affects the size estimate through the formula's quality/100 term -- lowering quality to 50 would roughly halve the JPEG estimate's quality-dependent factor, illustrating the direct trade-off between JPEG quality setting and resulting file size.

Related image-format and file-size tools

For checking whether WebP or AVIF format is safe to use for a given audience's browsers, the WebP/AVIF Compatibility Cheatsheet is directly relevant to the format choice this estimate compares.

For estimating how long a file of this size would take to download over a given connection, the Data Transfer & Download Time Calculator is a natural next step.

Frequently Asked Questions (FAQ)