Image Resizer

The Image Resizer is a free online tool to resize photos, screenshots, and graphics to exact dimensions — by pixels, percentage, or target file size. Works with PNG, JPG/JPEG, WebP, GIF, and BMP files. Resize a single image or drop dozens at once for batch processing. Lock aspect ratio to avoid distortion, or force exact dimensions when you need them. Every image is processed entirely in your browser using the HTML5 Canvas API — no file is uploaded to any server, no watermark is added to your output, and there are no size limits beyond your browser's memory.

Resizing images is one of the most frequent tasks in web development, digital marketing, and content creation. Every social network, ecommerce platform, and CMS has its own ideal dimensions: Instagram posts at 1080×1080, Twitter headers at 1500×500, Facebook covers at 820×312, Amazon product images at 2000×2000, email hero images at 600 wide. Doing this in Photoshop is overkill. Doing it online usually means uploading private photos to strange websites. This tool resizes instantly, privately, and without installing anything — perfect for batch-resizing product photos, preparing social media assets, shrinking screenshots for bug reports, creating thumbnails, or simply reducing a photo's file size before emailing.

The resizer uses the HTML5 Canvas API (CanvasRenderingContext2D.drawImage()) to scale images with the browser's built-in image interpolation. Modern browsers offer three quality levels via imageSmoothingQuality: low, medium, high. This tool defaults to high for best quality on downscaling (shrinking), which uses a form of bilinear or bicubic interpolation depending on the browser.

Aspect ratio:

- Locked (default) — changing width automatically adjusts height to maintain the original proportions. Prevents distortion.
- Unlocked — set exact width and height independently. Useful when the aspect ratio does not matter (fixed-size icons, banner crops).

Resizing modes:

- By pixels — specify exact target width and/or height.
- By percentage — specify a scale factor (e.g., 50% = half size).
- Fit to box — maximum dimension, with aspect preserved (e.g., longest side ≤ 1920).
- Fill box / crop — output exactly match target dimensions, cropping to fit.

Output format:

- PNG — lossless, supports transparency. Best for graphics with solid colors, screenshots, logos.
- JPG / JPEG — lossy, smaller files. Best for photos. Configurable quality 1-100 (85-95 is visually indistinguishable from original).
- WebP — newer format, ~25-35% smaller than JPG at same quality. Good browser support (2020+). Supports both lossy and lossless plus transparency.

Quality vs file size:

- JPG at quality 95: visually identical to original, ~20-40% smaller than 100.
- JPG at quality 85: very slight artifacts visible on close inspection, 2-3× smaller.
- JPG at quality 75: visible artifacts on detail-heavy areas, 4-5× smaller.
- PNG file size depends on color count and compression level, not a "quality" setting.
- WebP produces ~30% smaller files than JPG at equivalent perceived quality.

Browser memory considerations:

The Canvas API needs to hold both the source and resized image in memory. A 50 MP source image at full RGBA needs ~200 MB RAM. Most browsers handle this fine; very large images may hit limits. For huge files (100+ MP), consider server-side processing.

Image Resizer vs Image Compressor: Resizer changes dimensions (width × height). Compressor reduces file size at same dimensions (by adjusting JPG quality or re-encoding). Often used together: first resize to target dimensions, then compress to target file size.

Client-side (this tool) vs server-side (TinyPNG, Compressor.io): Client-side means your images never leave your browser — private, fast, no upload time. Server-side services typically have better compression algorithms (MozJPEG, zopflipng) but upload/process/download takes time and puts your photos on someone else's server.

Canvas API vs Photoshop / Affinity Photo: Desktop photo editors give you full creative control, masks, non-destructive edits. Canvas-based tools like this are for quick resizing tasks. If you are resizing > 1 image or need high quality for professional photography, use a proper editor.

Resizing vs cropping: Resizing changes all dimensions proportionally. Cropping removes parts of the image to change the aspect ratio. Use our Image Cropper for cropping-specific tasks.

JPG vs PNG vs WebP output: JPG for photos (lossy but small). PNG for graphics with transparency or few colors (lossless, larger). WebP for web (smaller than JPG at same quality). AVIF is the newest format — even smaller but less supported.

Aspect ratios: 1:1 (square, Instagram, profile), 16:9 (HD video, YouTube), 4:3 (classic TV, some cameras), 3:2 (DSLR standard), 9:16 (vertical, stories/reels), 2:1 (Twitter in-tweet), 1.91:1 (Facebook, OG image).