How to Resize an Image

· 2 min read

Resizing sounds simple, yet it trips people up constantly: stretched faces, blurry enlargements and photos rejected by forms for being “the wrong size”. A little understanding goes a long way.

Pixels and aspect ratio

A digital image is a grid of pixels, described as width × height — for example 1920 × 1080. The aspect ratio is the shape of that grid: 1920 × 1080 is 16:9, a typical widescreen shape.

When you resize while keeping the aspect ratio, width and height change together and the picture keeps its shape. If you set both numbers independently to something with a different shape, the image is stretched or squashed.

How to resize with Felx

  • Open the Image Resizer and choose your image. Its current size is filled in.
  • Type a new width; with “Keep aspect ratio” ticked, the height updates automatically. Or tap 25%, 50% or 75%.
  • Need an exact shape, like a square? Untick “Keep aspect ratio” and enter both numbers.
  • Select Resize image and download.

Changing the shape without stretching

If a form wants a square photo but yours is rectangular, stretching it will distort your face. Crop it to a square first — your phone’s built-in photo editor does this well — and then resize to the exact pixel size required.

Making images bigger

Enlarging cannot invent detail that the camera never captured, so big increases look soft. Small enlargements (up to around 150 percent) are usually acceptable; beyond that, find a larger original if you can.

Common sizes

  • Square social media post: 1080 × 1080
  • Full HD wallpaper or slide: 1920 × 1080
  • Website hero image: around 1600 to 2400 pixels wide
  • Email attachment photo: around 1600 pixels on the longest side

Centimetres, inches and DPI

Forms sometimes give sizes in centimetres, such as a 3.5 × 4.5 cm passport-style photo. To convert, you need the resolution (DPI, dots per inch); 300 DPI is standard for print.

Pixels = centimetres × DPI ÷ 2.54

So 3.5 cm × 300 ÷ 2.54 ≈ 413 pixels, and 4.5 cm × 300 ÷ 2.54 ≈ 531 pixels. Always follow the exact numbers given by the organisation if they specify pixels directly.

Resizing to meet a file size limit

Smaller dimensions mean a smaller file. If a resized image is still over the limit, finish with the Image Compressor.