Why images are so large in the first place
Cameras and phones capture far more detail than a screen shows. A 12-megapixel photo contains millions of pixels, and at full quality each one is stored with little compromise. On a web page that photo might be displayed at 800 pixels wide — less than a quarter of its original width — so most of that data is never seen. Resizing before compressing is therefore the biggest single saving: shrink the dimensions first, then compress what remains.
File size also depends on content. A photo of a busy street compresses less well than a plain sky, because there is more detail to preserve. That is why there is no single “best” quality setting for every image; the right setting depends on what the picture contains and how large it will be displayed.
Choosing the right format
Use JPG for photographs and complex images with many colours. JPG is lossy, which means it discards some detail, but at moderate settings that detail is mostly invisible. Use PNG when you need transparency or perfectly sharp text and line art, such as logos and screenshots — PNG is lossless, but photographic PNG files are usually much larger than JPG. WebP is the modern middle ground: it supports both photographs and transparency, and typically produces smaller files than JPG at the same visible quality, though very old software may not support it.
A practical rule: photographs to JPG or WebP, graphics with transparency to PNG or WebP, and anything with text you must keep razor-sharp to PNG. If a platform you use does not accept WebP, JPG is the safe fallback for photos.
How much compression is safe?
For JPG, a quality setting around 75 to 85 is a good starting point for web use; below about 60, blocky artefacts usually start to appear in skies, skin and smooth gradients. For WebP, similar visible quality often comes at a lower file size, so you can aim a little lower. Always compare the compressed version at 100 percent zoom — the size it will actually be viewed at — rather than zoomed in, where every format looks worse than it will in practice.
Text and sharp edges suffer first. If your image contains small text, a logo, or fine lines, be more conservative, or keep that image as PNG. For a large hero photograph, you can usually push compression further, because viewers look at the whole picture rather than inspecting individual pixels.
A workflow that works
Start from the original, never from an already-compressed copy — every round of lossy compression discards more detail, and you cannot get it back. Resize to the largest size the image will actually be displayed at, plus a little margin for high-resolution screens, then compress and check the result. Keep the original file safe, and export the compressed version under a different name so you can always redo it.
Check three things before publishing: the file size, the appearance at display size, and the format. A hero image under about 200 kilobytes is a reasonable target for most pages; a thumbnail should be far smaller. If the compressed image looks fine at display size and the file is small, you are done — chasing a few extra kilobytes at the cost of visible damage is not worth it.
Common mistakes
The most common mistake is uploading the full-size original and letting the platform shrink it in the browser — the visitor still downloads the whole file. Another is compressing the same image repeatedly, for example by saving a JPG, opening it, and saving it again at lower quality. A third is choosing PNG for a photograph out of habit, which can easily make the file five to ten times larger than an equivalent JPG.
Finally, remember that compression does not fix a bad photo. If the original is blurry, noisy or poorly lit, a smaller file will still be blurry, noisy or poorly lit. Fix exposure and sharpness first, then compress.
Try the related tools
Try the Image Compressor on Daily Tools. Try the Image Resizer on Daily Tools. Try the JPG/PNG/WebP Converter on Daily Tools.
Frequently asked questions
What is a good file size for a web image?
There is no single answer, but aim for under about 200 KB for a large photo and far less for thumbnails. The display size matters more than the original size.
Is WebP better than JPG?
For most photos, yes — WebP usually gives the same visible quality at a smaller file size, and it also supports transparency. Use JPG as a fallback for older software.
Does compressing an image twice damage it?
Yes, if the format is lossy like JPG. Each save discards more detail, so always compress from the original, not from an already-compressed copy.