How to Reduce Image File Size

· 2 min read

Upload forms with a 100 KB limit, emails that bounce, websites that load slowly — large images cause all of these. There are three ways to make an image smaller, and they work best in combination.

1. Reduce the dimensions

The number of pixels has the biggest effect on file size. A modern phone photo might be 4000 × 3000 pixels — 12 million pixels. Most screens show far less than that. Halving the width and height leaves a quarter of the pixels, and the file shrinks accordingly.

Typical sizes that are more than enough:

  • Email and messaging: 1600 pixels on the longest side
  • Website images: 1200 to 2000 pixels wide for full-width photos, less for smaller images
  • Profile pictures: 400 to 800 pixels square
  • Application form photos: whatever the form specifies, often around 200 to 600 pixels

Use the Image Resizer and keep “aspect ratio” ticked so the picture is not stretched.

2. Lower the quality setting

JPG and WebP are lossy formats: they discard detail your eye is unlikely to notice. A quality of 70 to 80 percent usually looks the same as the original at normal viewing size but is a fraction of the file size. Below about 50 percent you will start to see blocky patches, especially in smooth areas like sky.

The Image Compressor lets you set quality with a slider and shows the size before and after.

3. Choose the right format

  • JPG — best for photographs. Small files, universally supported.
  • PNG — best for screenshots, logos and graphics with sharp edges or transparency. Lossless, so photos saved as PNG are very large.
  • WebP — a modern format that is typically 25 to 35 percent smaller than JPG at similar quality, and supports transparency.

A photo saved as PNG is one of the most common causes of oversized images. Converting it with PNG to JPG can cut the size by 80 percent or more.

Hitting an exact size limit

If a form demands, say, under 50 KB:

  • First resize to the dimensions the form asks for, or something modest like 600 pixels wide.
  • Then compress, starting at 80 percent quality and lowering step by step until you are under the limit.
  • Check the final image still looks clear — especially faces and text.

A bonus: privacy

Photos from phones often contain hidden metadata, including the GPS location where they were taken. Re-saving an image with Felx removes this information, which is worth doing before posting photos publicly.