Resize by pixels or by percentage
Every digital image is a grid of pixels. A phone photo might be 4000 × 3000 pixels, while a website banner may only need 1200 × 900. Resizing changes that grid. Choose pixels when a website or form tells you an exact size, and percentage when you simply want the picture smaller, for example 50% to halve the width and height.
Keep the aspect ratio to avoid stretching
The aspect ratio is the shape of the image: 4:3, 16:9, 1:1 and so on. With “keep aspect ratio” on, changing the width updates the height automatically so faces and text are never squashed. Turn it off only when you need an exact size and don't mind the stretch, or use the Image Cropper first to cut the picture to the right shape.
Common sizes people need
| Purpose | Size in pixels |
|---|---|
| Instagram square post | 1080 × 1080 |
| Facebook or LinkedIn link image | 1200 × 630 |
| YouTube thumbnail | 1280 × 720 |
| Full-width website image | 1600–1920 wide |
| Blog image inside the text | 800–1200 wide |
| Email signature logo | about 300 wide |
For printed photos and passport pictures the size is usually given in millimetres or inches. At 300 DPI, 1 inch is 300 pixels, so a 2 × 2 inch photo is 600 × 600 pixels and a 35 × 45 mm photo is about 413 × 531 pixels. Always check the exact rules of the office you are applying to.
Resizing to make a file smaller
Fewer pixels means a smaller file. Halving the width and height leaves a quarter of the pixels, so the file often drops to a quarter of its size or less. For the smallest file, resize first and then use the Image Compressor.
Can I make a small image bigger?
You can, but the computer has to invent the missing pixels, so a 300-pixel image enlarged to 1200 pixels will look soft. If you need a large version, go back to the original photo when you can.