Why is my photo so large?

1. Too many pixels

This is the usual culprit. A 48 MP phone camera produces an 8000×6000 image — 48 million pixels for something that will be viewed in a 1000 px column or a chat bubble. File size scales with pixel count, so halving both dimensions removes three quarters of the data before any compression is applied.

Fix: resize to the largest size the image will ever be displayed at, then stop.

2. The wrong format for the content

A screenshot saved as PNG is efficient. A photograph saved as PNG is enormous, because lossless compression relies on repetition and photographs barely repeat. The same works in reverse: a screenshot saved as JPG is both bigger than the PNG and visibly worse around text.

Fix: match the format to the content — see PNG vs JPG vs WebP — then convert to JPG or convert to WebP as appropriate.

3. Quality set too high

Exporting at JPG quality 100 can double the file against quality 85 while producing a difference nobody sees outside a pixel-peeping comparison. The curve is steeply diminishing at the top end.

Fix: compress at 80 and compare against the original. Drop lower only until you can see the difference, then go one step back.

4. Detail the encoder cannot throw away

Some photos are genuinely expensive. Grain from a high-ISO night shot, foliage, gravel, water, fabric texture: fine random detail is incompressible, because there is no pattern to exploit and no smooth area to simplify. A noisy indoor photo can be several times the size of a clean studio shot at identical dimensions and quality.

Fix: accept it, or resize further. A smaller version of a noisy photo compresses much better because the noise is averaged away in the downscale.

5. Metadata and embedded extras

Usually minor but occasionally not: EXIF blocks, GPS coordinates, colour profiles, and — the big one — an embedded JPEG thumbnail or preview. Some cameras and editors attach a full-resolution preview inside the file, which can account for a surprising share of a file that seems too big for its dimensions.

Fix: strip the metadata. Worth doing anyway before publishing a photo publicly, since the GPS tag records where it was taken.

A quick diagnosis

1. Check the pixel dimensions first. Over about 2500 px on the long edge for screen use? Cause 1 — resize.
2. Is it a PNG of a photograph? Cause 2 — convert.
3. Reasonable dimensions, JPG, still several MB? Cause 3 or 4 — compress and watch how much it actually drops. Barely moves at quality 70? That is noise, not a setting.
4. Small dimensions but a surprisingly big file? Cause 5 — check the metadata.