WebP is 64% Smaller Than JPG at Q80
On June 18, 2026, I ran 17 image conversions on Convertify's production server (Rust + libvips 8.15). The test set: 26 PNG images (screenshots, illustrations, photos) and 24 iPhone HEIC photos. Every number below is measured, not estimated.
JPG to WebP Q80: 61 KB vs 171 KB source — a 64% reduction. Encode time: 0.19s vs 0.07s for JPG. Visual quality: nearly identical.
JPG to AVIF Q63: 55 KB — 68% smaller, but encodes in 1.30s (7x slower than WebP).
PNG to WebP Q80: 59 KB from 742 KB — 92% smaller. Same reduction as AVIF, but WebP encodes in 0.21s vs 1.49s.
HEIC to JPG Q85: 2,938 KB from 2,557 KB — a 14% increase. HEIC's HEVC codec is more efficient than JPEG's. To shrink iPhone photos, convert to WebP (43% smaller) or AVIF (57% smaller).
AVIF vs WebP: Speed Decides
At comparable quality (WebP Q80 vs AVIF Q63), file sizes are 61 KB vs 55 KB — a 10% gap. But encode time: 0.19s vs 1.30s. For a single image, negligible. For batch processing thousands, it's hours.
At aggressive compression, AVIF wins: AVIF Q50 at 33 KB beats WebP Q60 at 41 KB by 20%. If you control the pipeline and can pre-encode, use AVIF. For real-time or on-demand conversion, WebP is the practical default.
Lossless WebP: Only for Lossless Sources
Converting JPG to lossless WebP inflates file size by 177% (474 KB from 171 KB). Lossless encoding reconstructs a full pixel grid from already-lossy JPEG data — pointless. Use lossless WebP only when source is lossless (PNG, TIFF).
PDF Rasterization: WebP Up to 76% Smaller Than JPG
A single PDF page at 300 DPI: JPG Q85 = 395 KB, WebP Q80 = 126 KB (68% smaller). At 600 DPI: JPG = 4.2 MB, WebP = 1.0 MB (76% smaller). PNG lossless at 600 DPI: 17 MB — reserve for OCR or archival.
Encoding Speed: The Hidden Cost
| Format | Avg Encode Time | Relative to JPG |
|---|---|---|
| JPG (libjpeg-turbo) | 0.07-0.09s | Baseline |
| WebP lossy | 0.18-0.21s | 2-3x slower |
| WebP lossless | 0.71-0.73s | ~10x slower |
| AVIF (libaom) | 1.23-1.49s | ~18x slower |
| HEIC decode + re-encode | 1.90-14.52s | Varies |
How to Reproduce
All conversions used libvips 8.15 with libjpeg-turbo, libwebp, libaom, libheif+libde265, and poppler. Metadata stripped. To reproduce: convert similar files through Convertify's tools (JPG to WebP, PNG to WebP, etc.).
What You Should Do
- For web images: convert to WebP Q80. Best balance of size and speed.
- For maximum compression with pre-encoding: use AVIF.
- Never convert HEIC to JPG expecting smaller files.
- Use lossless WebP only for lossless sources.
- For PDF rasterization, 300 DPI WebP is the sweet spot.
