How to resize an image
Choose exact dimensions or Fit within box. Exact mode can lock aspect ratio; Fit within box always preserves it. Enlargement is off by default and must be enabled explicitly. Processing happens in the current browser tab.
Pixel dimensions are not the same as file size
Resizing changes the number of pixels. Compression changes how those pixels are encoded. A photo can have modest file size yet still be unnecessarily wide for a web layout, or it can have correct dimensions but inefficient encoding.
For example, reducing a 2400 × 1600 image to 1200 × 800 keeps the same 3:2 aspect ratio while cutting the pixel count from 3.84 million to 0.96 million. If the destination only needs the smaller display size, that reduction often matters more than lowering quality on the original dimensions.
Use the Image Compressor after resizing when the new pixel dimensions are correct but the byte size is still too high. The image size, format, and quality guide covers the full sequence.
Fit within a box
Fit within box treats the entered width and height as maximum bounds. A 1200 × 600 source fitted inside 300 × 300 becomes 300 × 150. The tool does not enlarge smaller sources unless Allow enlargement is enabled.
Keep the aspect ratio unless distortion is intentional
With the aspect-ratio lock on, changing one dimension recalculates the other so circles stay circular and faces are not stretched. Unlock it only when the destination explicitly requires dimensions that do not match the source ratio and distortion is acceptable.
If the destination requires a different shape without distortion, crop first with Image Cropper and then resize the cropped image.
Upscaling does not restore missing detail
Increasing width or height creates more pixels through browser resampling, but it cannot recreate detail that was absent from the source. Upscaling may satisfy a dimension requirement, yet the result can still look soft. Inspect the exported image at its intended viewing size rather than judging only the numeric dimensions.
Privacy and resource limits
The source image is decoded and resized locally; it is not uploaded for processing. Temporary preview URLs and decoded image data still occupy browser memory while the workspace is active. Inputs and outputs are limited to 20 MB, 8,192 pixels per side, and 16 megapixels, and supported browsers move the transform to a local worker. Animated PNG/WebP inputs are rejected because resizing one frame would silently remove animation.
For more context on the data path, read What browser-local file processing means.