Large images are the single biggest cause of slow web pages. They blow up your load time, hurt your Core Web Vitals, and on mobile they burn through your visitors’ data. The good news: most images are two to five times bigger than they need to be, and you can fix that without anyone being able to tell.
This guide walks through how to compress images so the file shrinks dramatically while the picture still looks pixel-perfect.
TL;DR — Compress photos to JPG or WebP at quality 75–80, keep graphics and screenshots as PNG or lossless WebP, and resize before you compress. You can do all of it for free in the bulk image compressor — nothing is uploaded.
Lossy vs lossless: what “without losing quality” really means
There are two kinds of compression, and knowing the difference is most of the battle.
| Type | Formats | What it does | Best for |
|---|---|---|---|
| Lossy | JPG, WebP, AVIF | Discards detail your eye won’t miss | Photographs, complex images |
| Lossless | PNG, WebP (lossless) | Stores the same pixels more efficiently | Logos, icons, screenshots, text |
“Without losing quality” doesn’t mean zero data is removed — it means none of the removed data is visible. A photo saved as JPG at quality 80 can be 70% smaller than the original while looking identical on screen. That’s the goal.
The quality slider, explained
Every lossy compressor has a quality setting from 1 to 100. It is not linear, and most people set it far too high.
- 90–100 — Near-lossless. Big files, marginal visual gain. Overkill for the web.
- 75–85 — The sweet spot. Major size savings, no visible artefacts on photos.
- 60–75 — Still fine for thumbnails and background images where detail matters less.
- Below 50 — Visible blocking and banding. Avoid for anything important.
The trick is to start low and move up only if you see a problem. Drop a photo into a compressor, set quality to 75, and compare it to the original at full size. Nine times out of ten you won’t be able to tell them apart — but the file is a fraction of the size.
Step by step: compress images the right way
- Resize first, compress second. A 6000px photo displayed at 1200px is wasting 80% of its pixels. Resize it to the size it will actually be shown before compressing — this alone often halves the file.
- Pick the right format. Photos → JPG or WebP. Graphics, logos, screenshots with text → PNG or lossless WebP. (See the format guide.)
- Set quality to 75–80 for photos and check the result against the original.
- Compress the whole batch at once. If you have a folder of images, do them together rather than one at a time.
- Verify the saving. A good tool shows the before/after size and the percentage saved, so you know it actually helped.
Tip: Switching a photo from JPG to WebP at the same quality typically saves another 25–35% on top of normal compression. If you only change one thing, change the format.
Do it now, in your browser
The fastest way to apply everything above is the free bulk image compressor. Drop in one image or a hundred, set the quality slider, and download the optimised files — or the whole batch as a zip.
Because it runs entirely on your device, there’s no upload wait, no file-size cap, and your images never leave your computer. It also refuses to make a file bigger: if an image is already well-compressed, it hands back the original untouched.
Common mistakes to avoid
- Compressing the same JPG repeatedly. Each lossy save degrades it further. Always go back to the original source.
- Using PNG for photographs. PNG is lossless, so photos stay huge. Use it only for graphics and transparency.
- Skipping the resize step. No compressor can fix an image that’s simply too large in dimensions.
- Trusting the number, not your eyes. Always eyeball the compressed result at full size before publishing.
Where to go next
- Smaller still? Convert your images to WebP or AVIF.
- Wrong dimensions? Resize images for the web.
- Need transparency? Remove an image background for free.