Compress JPG

Reduce the size of a JPG without sending it anywhere. The encoder here is MozJPEG, the same one used by the tools professional teams reach for, compiled to WebAssembly and running inside this tab.

Recompressing a JPG is a second loss

This is the fact that separates compressing a JPG from compressing anything else. Your file has already been through lossy compression once. Decoding and re-encoding it does not go back to the original image — it compresses an already-degraded copy, and the damage accumulates.

The practical rule is to do it once, at the lowest quality you can accept, rather than repeatedly nudging the slider down. Two passes at quality 80 look worse than one pass at 70 and usually save less space.

A real size cliff at quality 90

JPEG stores brightness and colour separately, and it normally stores colour at half resolution — a trick called chroma subsampling that works because human vision is far more sensitive to brightness detail than colour detail. Above a certain quality, encoders switch to storing colour at full resolution, and the file jumps.

We measured exactly where. On a 1600×1000 photograph the output goes 61 KB at quality 70, 72 KB at 75, 82 KB at 79 — then jumps to 114 KB the moment quality reaches 80 with automatic subsampling left on. Forcing half-resolution colour at that same setting gives 88 KB instead.

Because a 39% size jump for one notch of the slider is not something a user can reasonably predict, we hold colour at half resolution up to quality 89 and only allow full-resolution colour from 90 upwards, where you have clearly asked for maximum fidelity. The table below reflects that behaviour.

Choosing a number

For photographs on a website or sent through a chat app, 70 to 80 holds up almost always. The default here is 75. For print or further editing, use 90 or above and accept the larger file. Below roughly 60, smooth areas such as sky and skin start to show blocking.

If the image is a screenshot, a diagram or contains text, JPEG is the wrong format entirely — it produces visible ringing around hard edges no matter how high you set the quality. Those belong in PNG or WebP.

Why there are no limits here

The well-known compression sites upload your file, process it on their hardware and send it back. Server time costs money, so the free tier gets rationed — one popular service caps free web uploads at 15 MB per file, another allows two tasks per hour and watermarks anything beyond that.

Nothing is uploaded here, so nothing needs rationing. No size cap, no quota, no watermark, no account. Open DevTools, watch the Network tab, and compress something.