How to Reduce Image Size Without Losing Quality
Big image files slow down websites, bounce back from email and get rejected by upload forms. The good news is that most photos can lose a large part of their file size before anyone can see a difference.
Three things decide how big an image file is: its dimensions, its format and its compression level. Change them in that order and you will get the biggest saving for the smallest loss in quality.
A real example
We ran one photo through our image compressor to show what each setting does. It was a JPG of a tiger, 1000 by 667 pixels, and the file was 135 KB to start with.
| What we changed | File size | Saving |
|---|---|---|
| Original JPG | 135 KB | None |
| JPG at 75% quality | 98 KB | 27% |
| WebP at 75% quality | 60 KB | 55% |
| JPG at 75% quality, 300 pixels wide | 13 KB | 90% |
Your results will differ, because every photo compresses differently. A second test photo, which had already been compressed, only went from 59 KB to 50 KB at the same quality. The pattern is what matters: format helps a lot, and reducing the dimensions helps most of all.
Step 1: Fix the dimensions first
This is the biggest saving, and people often skip it. A phone photo can be 4000 pixels wide, but a blog post rarely shows an image wider than about 1200 pixels. Every extra pixel is data that nobody sees.
Halving the width and height leaves a quarter of the pixels, so resize before you do anything else. To choose a width, look at where the image will appear. A full-width banner needs far more pixels than a small thumbnail. If you want an image to stay sharp on high-resolution phone screens, a common rule of thumb is to use about twice the width it is shown at.
Step 2: Choose the right format
| Format | Best for | Transparency |
|---|---|---|
| JPG | Photos | No |
| PNG | Logos, screenshots, graphics with sharp edges | Yes |
| WebP | Nearly everything on the web | Yes |
According to Google’s WebP documentation, lossy WebP images are 25 to 34% smaller than comparable JPGs at the same quality, and lossless WebP images are 26% smaller than PNGs. All modern browsers can show WebP. If your image needs to open in older software, JPG is still the safe choice for photos.
Avoid saving photos as PNG. PNG keeps every detail exactly, which suits a logo but makes a photo very large. The opposite mistake is saving a screenshot as JPG, which leaves smudges around text.
Step 3: Set the compression level
For JPG and WebP, a quality setting of 70 to 80 percent is a good starting point for photos. At much lower settings, you will start to notice blocky patches and blur around edges. Faces, skies and smooth gradients show problems first, so check those areas.
Check the result at the size people will actually see it, not zoomed in to 400 percent. If you can’t tell the two versions apart at normal size, your visitors won’t be able to either.
How small should your images be?
There is no official size. These are rules of thumb that work well in practice:
- Website photos: under 200 KB each
- Large website banners: under 400 KB
- Email attachments: under 1 MB each
- Online application forms: use the limit stated on the form
If a form asks for a very small file, such as 100 KB, reduce the width first and then lower the quality. Lowering only the quality usually gives a worse-looking result than a smaller, cleaner image.
Common mistakes
Compressing the same image repeatedly. Each time you save a JPG, it loses a little more detail. Keep your original and always compress from that copy.
Trusting the file name. Renaming photo.png to photo.jpg doesn’t convert it. Use a tool that really changes the format.
Forgetting about location data. Phone photos can contain the place they were taken. When our tool compresses an image, those details are removed. If it can’t make a file any smaller, it keeps your original file instead, so that file still contains its details.
Quick checklist
- Keep a copy of the original.
- Resize it to the largest size it will be shown at.
- Pick WebP for websites, or JPG if it must work everywhere.
- Start at 75% quality and check the result.
- Only go lower if you still need a smaller file.
When you are ready, try it with the free image compressor. It works in your browser, so your images are not uploaded.