Resize an Image
Pick an image, set a size — it's resized in your browser, nothing is uploaded.
Resize an image in your browser
Pick an image, type a width (and optionally a height), and get a resized copy instantly. The resizing runs entirely in your browser with ffmpeg compiled to WebAssembly — your image is never uploaded to a server.
Fit modes
- contain (default) — fit inside the box, keep aspect ratio.
- cover — fill the box, keep aspect ratio, crop the overflow (needs both width and height).
- stretch — force the exact width × height, ignoring aspect ratio.
Tips
- Give only a width (or only a height) to scale proportionally.
- Works offline once the page has loaded.
FAQ
Do I need to fill in both width and height?
No — give just one and the other dimension is computed automatically to keep the aspect ratio. At least one of the two is required, and both must be positive. The only mode that insists on both is cover, because it has to know the full box to crop into.
When should I use contain, cover, or stretch?
contain (the default) fits the whole image inside your box without distortion, so the result can be smaller in one dimension. cover fills the box exactly and crops whatever overflows — ideal for thumbnails and hero images. stretch forces the exact width × height and will distort the picture if the aspect ratio differs.
Does resizing convert my image to another format?
No — the output keeps the input's format: a .jpg in gives a .jpg out, a
.png stays .png. The file is re-encoded at the new size by ffmpeg, so the
resized copy is a fresh encode rather than a metadata-only change.
Is my photo uploaded anywhere while resizing?
No. The whole pipeline is ffmpeg compiled to WebAssembly, running inside your browser tab. The image never leaves your device, and once the page has loaded the tool keeps working without a network connection.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool image-resize 'url=https://example.com/input' 'width=640' 'fit=contain'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/image-resize/?url=https://example.com/input&width=640&fit=containMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.