File size follows area, not the side
Works out the second dimension when the first changes, gives the scale as a percentage, and estimates what happens to the file size.
The commonest mistake when shrinking images: 'half the size means half the file'. In fact the file follows pixel count, which is area — halving each side quarters the file.
You can drive it by any of four values here: the new width, the new height, the long side, or a percentage — and the rest follows with the proportions intact.
What this calculator shows
- Both dimensions of the new size, proportions preserved
- The scale as a percentage of the original
- An estimate of the file size after resizing
What to keep in mind
- The size estimate assumes the compression level stays put; in practice JPEG compresses slightly more efficiently at small sizes.
- Enlarging adds pixels but not detail: a scale above one hundred percent buys nothing real.
FAQs
How do I resize a photo without distorting it?
Set one side and derive the other from the original proportion. Setting both sides independently stretches the image.
How much smaller does the file get?
Roughly in proportion to the drop in area. Halving each side gives a file about a quarter of the size.
What size should I use for a website?
1920 pixels on the long side covers nearly any screen. Product cards and thumbnails are fine at 800 to 1200.
Can I enlarge an image without losing quality?
Not with ordinary interpolation, which only blurs the pixels already there. Neural upscalers invent plausible detail, but invent it they do.
Worked example
A photo for the web
Input: 4000 × 3000 → width 1920
Output: 1920 × 1440, which is 48% of the original
Note: The pixel count fell by a factor of 4.3, and the file falls by roughly the same. The side only halved — that gap is the whole source of the confusion.