How to Convert and Compress Images Online
The Bulk Image Converter lets you transform images between JPEG, PNG, and WebP formats while controlling compression quality and output dimensions. Upload your images, choose your settings, and download all converted files as a single ZIP archive. The entire process runs in your browser — no uploads, no accounts, no waiting.
Start by uploading your images. The tool accepts JPEG, PNG, WebP, GIF (first frame), and BMP input formats. Once loaded, a thumbnail preview grid shows each image with its current dimensions and file size, so you can see the starting point before conversion.
Select your target format from the dropdown. JPEG produces the smallest files for photographs but does not support transparency. PNG preserves transparency and produces lossless output but results in larger files. WebP offers the best of both worlds — lossy compression for photographs and lossless compression for graphics, with transparency support and 25-35% smaller files than JPEG.
Adjust the quality slider to control the compression level. Lower quality means smaller files but more visible artifacts. For web publishing, 80-85% is the optimal balance. Optionally set maximum width and height dimensions to downscale images — the tool preserves aspect ratio automatically, so you never get stretched or squished output.
Understanding Image Formats: When to Use Which
JPEG uses lossy compression that discards visual information the human eye is least likely to notice. It excels at photographs and complex images with smooth color gradients. JPEG does not support transparency. A typical JPEG at 85% quality is 5-10x smaller than the equivalent PNG. Use JPEG for: product photos, blog post images, social media content, email attachments.
PNG uses lossless compression that preserves every pixel exactly. It supports transparency (alpha channel), making it essential for logos, icons, UI elements, and any graphic that needs to overlay other content. PNG files are significantly larger than JPEG for photographs because lossless compression cannot exploit the visual redundancy in photographic content. Use PNG for: logos, icons, screenshots, graphics with text, images requiring transparency.
WebP is a modern format developed by Google that supports both lossy and lossless compression, transparency, and animation. WebP lossy files are 25-35% smaller than JPEG at equivalent quality. WebP lossless files are 26% smaller than PNG. Every major browser supports WebP natively — Chrome, Firefox, Edge, Safari (since 14.0), and Opera. Use WebP for: any web image where you want the smallest file size without sacrificing quality.
AVIF is the newest format (based on the AV1 video codec) offering even better compression than WebP — up to 50% smaller than JPEG. However, browser support is still growing and encoding is slower. For maximum compatibility in 2026, WebP remains the safest choice for broad deployment.
Why Image Compression Matters for Web Performance
Google's Core Web Vitals — the metrics that directly influence search rankings — include Largest Contentful Paint (LCP), which measures how quickly the main content of a page becomes visible. Images are the most common LCP element. A 2MB hero image that could be 400KB in WebP format adds over a second of load time on a 3G connection.
The HTTP Archive reports that images account for approximately 50% of total page weight across the web. Converting from PNG to WebP, reducing JPEG quality from 100% to 85%, and resizing images to their display dimensions are the three highest-impact optimizations most websites can make.
This tool lets you apply all three optimizations in a single batch operation. Convert your images to WebP, set quality to 82%, and constrain dimensions to your maximum display size. The result is a set of web-optimized images that load fast, look great, and improve your search rankings.
Frequently Asked Questions
JPEG for photographs, PNG for graphics and transparency, WebP for the best compression across all use cases. If you can only pick one format for a modern website, choose WebP — it is supported by every major browser and produces the smallest files.
80-85% for JPEG and WebP is the optimal range for web use — visually identical to 100% but dramatically smaller. For archival or print, use 95%+. For thumbnails and previews where quality is less critical, 70-75% saves significant bandwidth.
Downscaling (making images smaller) generally improves perceived quality by averaging pixel values. The tool uses the browser's built-in image scaling algorithms, which produce smooth results. Upscaling (making images larger) will appear blurry because standard interpolation cannot create detail that doesn't exist.
No. All conversion, compression, and resizing happens in your browser using the Canvas API. Your images are loaded into memory, processed locally, and packaged into a ZIP file using JSZip. No data is transmitted over the network.
There is no artificial limit. Practical limits depend on your device's available memory. Modern browsers can handle images up to 16384x16384 pixels. For very large batches of high-resolution images, process in groups of 20-30 to avoid memory pressure. The tool processes images sequentially to minimize peak memory usage.