Image resizer
Resize images by pixel dimensions or percentage, lock the aspect ratio, enable high-quality interpolation, and compare original vs. output size.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Images are resized locally in your browser and never uploaded
High-quality interpolation looks smoother when enlarging, at a small speed cost.
Pick an image first
The output size, file size and scale show up here after exporting.
What this tool does
- Turn a 4K photo into a 1920px web asset and see the target size, scale factor and real output file size before you download it.
- Think in percentages: ask what 25% means in pixels and the tool answers 1920 × 1080 → 480 × 270 immediately.
- Change one edge and let the other follow: lock the aspect ratio, type a width and the height is derived from the original so nothing gets stretched.
- Sanity-check before uploading: identical dimensions are flagged as "no change" and enlarging warns that the image will go soft.
Example
Input
Original 1920 × 1080 resized to 25%, exported as photo.png
Output
480 × 270 Filename photo-480x270.png
The percentage formula multiplies each edge by percent/100, rounds it and keeps at least 1px, so 1920 × 25% = 480 and 1080 × 25% = 270. Output names follow "base name + -widthxheight.extension". The actual redraw and export use the browser canvas and cannot be verified offline.
Frequently asked questions
Will enlarging keep the image sharp?
No. Enlarging interpolates pixels that never existed, so the image softens, and the tool warns when the target exceeds the original. High-quality interpolation only makes the result smoother without recovering detail — re-export from the original asset if you need a bigger file.
When should I turn off "lock aspect ratio"?
It is on by default, so changing the width updates the height and the image is never squashed. Turn it off only when you deliberately want a stretched result, such as forcing a placeholder into a fixed frame; then width and height can be set independently.
Which interpolation quality should I choose?
The three options map to canvas imageSmoothingQuality: high looks smoother on enlarged and heavily downscaled images but is slightly slower, medium is the default trade-off, and low is fastest for previews and bulk drafts. The output file size barely changes between levels — the difference is visual.
Is there a maximum dimension?
Each edge is capped at 20000 pixels, the practical browser canvas limit; beyond that most devices fail to allocate the bitmap. Even under the cap a huge canvas consumes a lot of memory, so process large images one at a time.
Are my images uploaded?
No. Images are decoded locally, drawn onto a canvas and turned into a Blob for download. The page has no upload endpoint and never stores your files.
Keywords：图片缩放调整尺寸resize imageimage resizer缩略图宽高比插值canvas resize