Resizing is really two different operations wearing one name
'Resize' covers two mathematically different actions: scaling, where width and height change together by the same ratio, and stretching, where they change independently. Scaling preserves the shape of everything in the image — a circle stays a circle. Stretching distorts it — a circle becomes an oval. Aspect-ratio lock is what decides which one you're doing: on, you're scaling; off, you're stretching, whether you intend to or not.
This distinction matters more than it sounds. A resize that looks 'slightly off' — faces a bit wider, a logo a bit squashed — is almost always an aspect-ratio mismatch, not a bad crop or a bad export. Getting the ratio right is the actual skill here; the pixel values are just numbers.
Aspect ratio lock: on vs off
| Setting | What happens when you change width | Use case |
|---|---|---|
| Locked (default) | Height auto-updates to preserve original proportions | Photos, logos, anything that shouldn't look stretched |
| Unlocked | Height stays exactly as entered | Filling an exact fixed slot (banner ad, form thumbnail) where the source ratio doesn't need to match |
Resizing an image
Drop your image onto the zone.
Enter the target width and height in pixels.
Toggle Lock aspect ratio to scale proportionally (this is on by default).
Choose an output format and click Resize & download.
Working out the right dimensions before you start
If you know the target width but not the height (or vice versa), aspect-ratio lock does that arithmetic for you — enter one dimension, and the other adjusts to match the original ratio automatically. This is faster and more accurate than computing it by hand, especially for odd source ratios like 1920×1050 rather than a clean 16:9.
What upscaling can and can't do
Enlarging an image beyond its original dimensions uses smoothing algorithms to interpolate new pixel values between existing ones — essentially educated guesses about what should go in the gaps. This produces a visually acceptable result up to a point, but it cannot recover detail that was never captured in the first place. A 500×500 photo upscaled to 2000×2000 will look softer and less crisp than a photo actually captured at 2000×2000, no matter how good the smoothing algorithm is.
As a rule of thumb, modest upscaling (under roughly 2x) tends to hold up reasonably well for photos; pushing much further starts to show visible softness, especially in fine detail like text or hair.
Common mistakes
Turning aspect-ratio lock off without meaning to, then wondering why faces or logos look subtly stretched.
Expecting upscaling to sharpen a low-resolution image — it smooths, it doesn't invent detail.
Targeting an extremely large canvas (well over 16 megapixels) and having the resize silently fail on some browsers due to memory limits.
Resizing down for file-size reasons alone when the goal is actually compression — resizing changes dimensions; use the Image Compressor if you want to keep the same dimensions but shrink the file.
Format choice affects more than just dimensions
The output format you pick alongside the resize matters for two reasons. First, downscaling generally reduces file size on its own since there are fewer pixels to encode, but the format and its quality settings still determine how much. Second, if your source image has transparency, keep that in mind when picking the output format — JPEG can't preserve it. For deeper control over compression quality after resizing, run the result through the Image Compressor, or convert between formats first using the Image Converter.
Real use cases
Resizing a phone photo down to exact pixel dimensions required by a job application or form upload.
Scaling a batch of product photos to a consistent width for a catalog, using aspect-ratio lock to avoid distortion across different source shapes.
Preparing a profile picture to fit an exact square dimension required by a platform.
Upscaling a small logo modestly for a slightly larger placement where slight softening is acceptable.
Frequently asked questions
Q: How does aspect-ratio lock work?
A: With it on, changing the width automatically updates the height (and vice versa) to keep the original proportions. Turn it off for free-form resizing where width and height change independently.
Q: Can I upscale an image?
A: Yes — enter dimensions larger than the original. Upscaling uses high-quality smoothing but can't add detail that wasn't captured in the source.
Q: What's the maximum size?
A: There's no hard limit set by the tool; your device's memory is the real bound, and very large canvases over roughly 16 megapixels may fail on some browsers.
Q: Does resizing reduce file size?
A: Usually yes when downscaling, since fewer pixels means less data to encode — though the output format and its quality settings also affect the final size.
Q: Are my images uploaded anywhere?
A: No. Resizing happens entirely in your browser using the Canvas API.
Q: I entered exact dimensions but the result still looks stretched — why?
A: Check whether aspect-ratio lock was on. If the target dimensions you entered don't match the original ratio and the lock was off, the image will stretch to fill exactly what you specified rather than scaling proportionally.
Resize your image now
Get exact dimensions with the Image Resizer. Need a smaller file size at the same dimensions? Try the Image Compressor. Need a different format? Use the Image Converter, or straighten and flip your image first with Rotate & Flip Image.
