Compress image online — smaller file, same look

When people search for “compress image” they usually want one thing: a smaller file that still looks like the original. Two things control a photo’s file size. The first is how many pixels it has — a 12-megapixel phone photo carries twelve million colour values. The second is how hard those pixels are packed when the file is saved.

JPG and WebP pack pixels by discarding detail your eye barely notices — tiny colour differences, fine texture in shadows. The Quality slider decides how aggressively. At 90 the file is large and practically identical to the source; at 80 it is roughly half the size and still looks the same on screen; below 50 blocks and smudges start to appear around edges and in smooth skies. PNG does not discard anything, which is why it has no quality slider and why photo-sized PNGs are huge.

The fastest saving is almost always to remove pixels nobody will see. Most screens are 1920 pixels wide or less, so a 4000-pixel photo shown on a web page is shrunk by the browser anyway — you are paying for pixels that are thrown away on arrival. Reduce the pixels first, then fine-tune the quality; that order gives the smallest file for a given look.

Tick Keep the file under, type the limit (or press the 200 KB, 500 KB, 1 MB or 2 MB button) and choose JPG or WebP. The tool starts at your quality setting; if the file is too big it tries lower qualities — at most seven encodes — and keeps the highest quality that fits. The number on the Download button is the size of that exact file, not an estimate.

Three details are worth knowing. First, the limit works on quality only: it never shrinks the pixels behind your back, so for a small limit such as 100 KB also type a smaller width (1200 px is comfortable) or the quality will have to drop until the picture looks blocky. Second, if your picture already fits under the limit at your quality setting, it is saved as is — it will not be inflated to “use up” the allowance. Third, the lowest limit you can enter is 10 KB, and PNG ignores the limit entirely, so switch to JPG or WebP first.

As a rule of thumb, a photo at quality 80 needs roughly 800 × 600 px to land near 100 KB, 1024 × 768 px near 200 KB, 1600 × 1200 px near 500 KB and 2048 × 1536 px near 1 MB. Photos with fine detail — foliage, fabric, noise from a dark room — need more bytes than a portrait in front of a plain wall, so treat these as a starting point. For limits of 20 KB and 50 KB, the ones found on application forms, see resize an image to 20 KB or 50 KB.

• Compressing a JPG twice. Every save at lower quality throws away a little more. Always go back to the original file and compress that once.
• Using JPG for screenshots and text. Sharp edges get a fuzzy halo of noise. Keep PNG for screenshots, or make the picture smaller in pixels instead.
• Lowering quality when you should lower pixels. A 4000-pixel photo squeezed to 100 KB looks blocky; a 1200-pixel photo at 100 KB looks clean.
• Going below quality 60 without checking. Open the preview; some images survive it, many do not.
• Sending WebP to a system that only knows JPG. If a form or an old program refuses the file, save as JPG.
• Enlarging by accident. Making a photo bigger than it was adds no detail and makes the file heavier. The tool warns you when a size is larger than the original.

The saved file is built from the picture’s pixels, so metadata such as camera model or GPS location is not carried over into it — a small privacy bonus when you share photos. Your original file on disk is never changed.