Image Resizer

Downscaling vs upscaling — they are not the same problem

Making an image smaller is the easy direction. Every four source pixels collapse into one output pixel, and the encoder averages them together — there's always more information than you need. Making an image bigger is the hard direction, because the resizer has to invent pixel values that weren't there. The best traditional algorithm (bicubic, which this tool uses through the browser's native Canvas API) looks at 16 neighbouring pixels and fits a smooth surface; AI "super-resolution" (Topaz Gigapixel, waifu2x, ESRGAN) goes further by hallucinating plausible detail. Neither gives you back information the camera didn't capture — it just extrapolates.

Aspect ratio and why you usually want to keep it

Aspect ratio is width ÷ height. A 3000×2000 photo has a 3:2 ratio. If you force it to 1920×1000 — roughly 1.92:1 — everything stretches horizontally and faces go strange. That's why this tool locks the ratio by default: type a new width and the height follows. Unlock only when you've already cropped to the target ratio, or you want the distortion on purpose.

Common sizes worth memorising

• Instagram square post: 1080 × 1080
• Instagram portrait: 1080 × 1350 (4:5)
• Instagram story / Reel: 1080 × 1920 (9:16)
• Twitter/X in-line image: 1600 × 900 (16:9)
• LinkedIn post image: 1200 × 627
• LinkedIn banner: 1584 × 396
• Facebook post: 1200 × 630
• YouTube thumbnail: 1280 × 720
• Open Graph / Twitter card: 1200 × 630
• Favicon: 32 × 32 (plus 16, 180, 512 for full coverage)
• Passport photo (UK): 45 × 35 mm at 300+ DPI
• Amazon main product image: minimum 1000 × 1000 (for zoom).

DPI is a print thing — ignore it on screen

There's a persistent myth that "72 DPI is for screen, 300 DPI is for print." DPI (dots per inch) only matters when an image is printed. A screen has its own pixel density and ignores the DPI field in the image metadata entirely. If you need a 4×6 inch print at 300 DPI, that's 1200 × 1800 pixels — resize to those pixel dimensions and the print looks fine regardless of what the DPI tag says. This tool only changes pixel dimensions, which is the only number that actually affects the image.

Tips for cleaner resizes

• Halve, don't eighth. Resizing in one big step is fine for Canvas, but if you ever hit stair-stepping at extreme downscales, resize to 2× the target first, then to the target.
• Sharpen after downscale. Every downscale softens edges. A mild unsharp mask pass in any editor cleans it up.
• Don't upscale more than 2×. Beyond that, even the best algorithm starts inventing detail that wasn't there. Source a bigger image instead.
• Save as PNG if the image contains text or UI. Resizing and re-saving as JPEG will smear letterforms.

Privacy

The image is decoded into a <canvas>, redrawn at the target dimensions with bicubic-quality interpolation, and exported back to a file — all in your browser. Nothing touches a server.