Image Resizer
Resize an image to exact dimensions or by percentage, entirely in your browser.
Runs entirely in your browser — nothing you enter is uploaded.
How to use Image Resizer
- Choose an image — its current dimensions are shown once loaded.
- Enter a new width; height follows automatically if "Keep aspect ratio" is ticked.
- Untick the ratio lock if you need an exact width and height, accepting some distortion.
- Click Resize, then download the result.
How this works
The image is drawn to a canvas at the target dimensions using the browser's built-in bilinear resampling, with high-quality smoothing enabled. Downscaling averages source pixels into each destination pixel, which is why reducing size is generally clean. Upscaling has to invent pixels that were never captured, so it can only interpolate between neighbours — the result is larger but not more detailed. Processing happens locally; the file is never uploaded.
height = width × (original height ÷ original width), when aspect ratio is locked
Assumptions
- Aspect ratio is preserved unless you explicitly unlock it, in which case the image will distort.
- Output is re-encoded, so lossy formats undergo one additional compression generation.
- Dimensions are in CSS pixels; device pixel ratio is not applied.
Worked example
A 4032 × 3024 photo resized to 1200px wide with ratio locked.
- Original
- 4032 × 3024
- Target width
- 1200 px
- Result
- 1200 × 900
The 4:3 ratio is preserved, so height follows automatically at 900px. This also cuts the pixel count by roughly 91%, which usually reduces file size far more than any compression setting would — resizing before compressing is almost always the bigger win.
How to read the result
Resize before compressing, not after: serving a 4000px image scaled down by CSS wastes bandwidth and hurts loading performance regardless of quality settings. For web use, match the largest size the image will actually be displayed at, then roughly double it only if you are targeting high-density screens. Avoid upscaling where you can — if you need a larger image, go back to the original source.
Limitations
- Upscaling cannot recover detail that was never in the original; it interpolates and softens.
- Uses the browser's standard resampling, not a specialised algorithm such as Lanczos.
- Very large source images may exceed available browser memory, particularly on mobile devices.
- Does not crop. Changing the aspect ratio stretches the image rather than trimming it.
Frequently asked questions
- Is my image uploaded anywhere?
- No. Resizing happens entirely in your browser via the canvas API — the file never leaves your device.
- Can I make an image bigger without losing quality?
- Not genuinely, no. Upscaling can only interpolate between the pixels that already exist, described above — it produces a larger file but not more real detail. If you need a bigger image, the original source has to be re-captured or re-exported at a higher resolution.
- What size should I use for a website?
- Match the largest size the image will actually be displayed at on the page, then resize before compressing rather than after — cutting pixel count first usually saves far more file size than any compression setting alone.