Batch Convert Images — JPG · PNG · WEBP
Convert many images at once between JPG, PNG, and WEBP — with a quality slider — and download everything as one ZIP. 100% in your browser: no upload, no signup. WEBP for smallest files, PNG for transparency, JPG for universal compatibility.
· Free forever · No registration
Batch image conversion means re-encoding many images between JPG, PNG, and WEBP in a single pass. Resizo's free batch converter runs entirely in your browser using the HTML5 Canvas API — no upload. Pick the output format, set quality (JPG and WEBP only; PNG is lossless), optionally cap the width to shrink files further, and download everything as a ZIP. WEBP is typically 25–35% smaller than JPG at matching quality.
Drop images to convert
or click to browse · JPG · PNG · WEBP · GIF
Format Comparison
| Format | Best For | Transparency | Avg Size |
|---|---|---|---|
| JPG | Photos, social posts | No | Medium |
| PNG | Logos, icons, screenshots | Yes | Large |
| WEBP | Web — best of both | Yes | Smallest (~30% less) |
Image Format Optimization & Batch Conversion Strategy
WebP Conversion & Core Web Vitals Performance
WebP compression delivers 25-35% smaller file sizes compared to JPG at equivalent visual quality, directly improving Largest Contentful Paint (LCP) and overall page load metrics. A website with 200 JPG images averaging 150 KB each (30 MB total payload) reduces to 9-12 MB when converted to WebP—translating directly to 2-4 seconds faster page loads on 4G networks. Google's Core Web Vitals algorithm ranks sites with faster LCP scores higher; a study of 1M+ sites shows WebP adoption correlates with 0.3 second average LCP improvement. Batch converting entire image libraries (50-500 images) takes minutes with automated tools vs. days of manual conversion. The trade-off: WebP support varies by browser (Internet Explorer, older Safari on iOS), so serving both JPG and WebP (with fallbacks) requires slightly more complex image serving logic that's worth the performance gain.
Transparency Conversion & Asset Pipeline Workflows
PNG files with transparency average 2-3x larger than JPG equivalents. Logo assets, UI components, and product cut-outs often exist as PNG with unnecessary whitespace and transparency. Converting these to optimized WEBP with transparency preserves quality while reducing file size 40-50%, particularly when transparency is sparse (logo on corner, not entire image). Design teams benefit from batch conversion workflows that automatically optimize asset libraries—reducing 500 PNG icons from 50 KB average to 15-20 KB average recovers 15+ MB of storage and CDN bandwidth. Conversion order matters: always convert from high-quality source (PNG or lossless WebP) to lower quality (JPG or lossy WebP), never upconverting from JPG to PNG (which adds size without recovering detail). Batch tools allowing quality parameter configuration enable teams to test multiple quality levels and pick the optimal balance—particularly critical for email and messaging assets where file size directly impacts delivery speed and storage costs.
Email & Messaging Optimization for File Size Constraints
Email clients (Gmail, Outlook) and messaging platforms (WhatsApp, Telegram) enforce strict file size limits: images over 5 MB are rejected or heavily compressed. Batch converting high-quality PNG screenshots to JPG at 75-85% quality reduces typical 4-6 MB screenshots to 400-600 KB—small enough for email while preserving text readability. Email recipients with slow connections (2G/3G) see rendering delays proportional to image payload; a 150 KB image loads in under 1 second on 4G but takes 8+ seconds on 2G. Batch conversion with max-width constraints (e.g., convert and resize to 800px width max) ensures images fit mobile viewports and load rapidly. Content teams managing 1000+ annual email campaigns benefit from automated conversion pipelines—manually converting each campaign's 10-20 images takes 30-60 minutes per campaign; batch tools reduce this to 2-3 minutes, enabling faster campaign turnaround.
When to batch-convert image formats
Faster websites
Convert a site's JPG and PNG library to WEBP to cut image payload by 25–35% with no visible quality loss. Directly improves Largest Contentful Paint (LCP) and PageSpeed scores.
Transparency needs
Convert JPGs to PNG (or WEBP) when you need transparent backgrounds — logos, UI assets, product cut-outs. Note: JPG doesn't store transparency, so source transparency must already exist.
Email & messaging
Convert heavy PNG screenshots to JPG at 75–85% quality to fit inside Gmail, Outlook, or WhatsApp limits. Pair with the optional max-width to hit a target file size.
Other Batch Tools
FAQ
Which format is smallest for the web?
WEBP is typically 25-35% smaller than JPG and PNG at the same visual quality, with transparency support.
Why is the quality slider hidden when I pick PNG?
PNG is lossless. Every PNG is encoded at maximum quality. To shrink a PNG, resize its dimensions or convert to WEBP.
Will converting JPG to PNG improve quality?
No. PNG is lossless but the source JPG already lost detail. PNG only freezes existing quality at a much larger file size.
Are my files uploaded?
No. Conversion runs entirely in your browser. Files never leave your device.