Websites, email newsletters, online stores and print shops all want images at specific sizes, and stretching a photo to fit makes people look wider or taller than they are. This calculator works out new dimensions that preserve the original aspect ratio, whether you start from a target width, a target height, a percentage, or a box the image must fit inside. It also shows the scale factor, the change in megapixels and the print size at any DPI.
How to use the image resize calculator
- Enter the original width and height in pixels.
- Choose how to resize: by new width, new height, percentage, or fit inside a box.
- Enter the target value(s).
- Optionally set a print resolution (DPI) to see how large the resized image prints.
- Read the new size on the tape; the table lists common scales for the same image.
Image resize formulas
Results are rounded to whole pixels, which can change the ratio by a tiny fraction of a percent; the tape reports that rounding error.
Worked example
A phone photo is 4032 × 3024 pixels (12.2 megapixels) and a blog theme wants images 1600 pixels wide.
- Scale factor: 1600 ÷ 4032 ≈ 0.3968 (39.68%).
- New height: 3024 × 0.3968 = 1200 pixels.
- New size: 1600 × 1200, still 4:3, now 1.92 megapixels — about 16% of the original pixel count.
- At 300 DPI it would print at 1600 ÷ 300 ≈ 5.33 by 1200 ÷ 300 = 4 inches.
Fitting a box instead: to fit the same photo inside 1920 × 1080, the width factor is 1920 ÷ 4032 ≈ 0.476 and the height factor is 1080 ÷ 3024 ≈ 0.357. The smaller factor wins, giving 1440 × 1080. Height is the limiting side, so the image fills the box’s height and leaves 240 pixels of width unused.
Typical target sizes
| Use | Common size (pixels) |
|---|---|
| Full-width website hero | 1920–2560 wide |
| Blog or article image | 1200–1600 wide |
| Email newsletter image | about 600 wide (1200 for high-DPI screens) |
| Social share preview (Open Graph) | 1200 × 630 |
| Square social post | 1080 × 1080 |
| 4 × 6 inch photo print at 300 DPI | 1800 × 1200 |
| 8 × 10 inch photo print at 300 DPI | 3000 × 2400 |
Note that 1200 × 630 is about 1.9:1, so a 4:3 photo must be cropped, not just resized, to fill it exactly. Resize first to the right width, then crop the height.
Resizing tips
Shrink once, from the original
Every resize resamples the pixels and loses a little detail. Keep the full-size original and make each smaller version directly from it rather than resizing a resized copy.
Mind file size as well as dimensions
Halving both dimensions cuts the pixel count to a quarter, which shrinks the file roughly fourfold. For the web, combine sensible dimensions with modern compression (WebP or AVIF) for fast-loading pages.
Provide 2× images for sharp screens
High-density displays show twice as many pixels per CSS pixel. An image displayed 800 pixels wide on a page looks crisp on these screens if the file is 1600 pixels wide.
For the ratio itself, or to find a missing dimension for 16:9 or another standard, use the aspect ratio calculator. To relate pixels to a screen’s physical sharpness, try the PPI calculator.
Frequently asked questions
How do I resize an image without distorting it?
Scale both dimensions by the same factor. Divide the new width by the old width to get the factor, then multiply the old height by it. A 4032 × 3024 photo resized to 1600 pixels wide has a factor of 1600 ÷ 4032 ≈ 0.3968 and a new height of 1200.
What does 'fit inside a box' do?
It finds the largest size that fits within a maximum width and height without cropping. The calculator computes a scale factor for each side and uses the smaller one, so the image touches the box on one side and stays inside on the other.
Will enlarging an image make it sharper?
No. Upscaling adds pixels by interpolating between existing ones, so no new detail appears and edges soften. Resizing down is safe; resizing up beyond about 120–150% usually looks noticeably soft.
What size should a photo be for printing?
Divide the pixel dimensions by the printer resolution. At 300 DPI, the common standard for photo prints, a 1600 × 1200 image prints at 5.33 × 4 inches. Lower resolutions such as 150 DPI are acceptable for posters viewed from a distance.