Short answer: resize the dimensions first, then compress. A 1200-pixel-wide image at 80% JPEG quality is a fraction of the original size and looks identical on any screen it will actually be viewed on.
Dimensions and file size are different things
This trips most people up. An image has two separate measures:
- Dimensions â how many pixels, e.g. 4032 Ã 3024
- File size â how many bytes on disk, e.g. 3.8 MB
A modern phone photo is around 12 megapixels. A full-screen photo on a laptop needs about 2 megapixels. You are carrying six times more detail than the display can show. Cutting dimensions is therefore almost free visually, and it is the most effective single step.
What size do you actually need?
| Use | Sensible width | Typical file size |
|---|---|---|
| Email attachment | 1200 px | 150â300 KB |
| Website / blog image | 1600 px | 200â400 KB |
| Social media post | 1080â2048 px | 300â600 KB |
| Printed 6Ã4 photo | 1800 px | 1â2 MB |
| Printed A4 | 2480 px | 2â4 MB |
| Archive / editing master | Keep original | â |
Note the last row. Resize a copy. Once detail is discarded it cannot be recovered, so never overwrite your only version of a photo you care about.
Doing it on the phone
iPhone: the Photos app has no resize function, which surprises people. You can crop, which reduces dimensions, but not scale. Workarounds: use Mail and choose a smaller size when attaching, or use an app or web tool.
Android: varies by manufacturer. Samsung Gallery has a resize option under the image detail menu; stock Android does not. Google Photos does not resize on export either.
Because both platforms are weak here, a dedicated image resizing app or a browser tool such as resize image is usually the fastest route.
Choosing a format
| Format | Best for | Avoid for |
|---|---|---|
| JPG | Photographs, anything with gradients | Text, logos, transparency |
| PNG | Screenshots, logos, transparency needed | Photographs â files get huge |
| WebP | Almost everything on the web | Sending to very old software |
| HEIC | iPhone storage efficiency | Uploading anywhere |
The single most common mistake is saving a photograph as PNG. A PNG of a photo can be five times larger than the equivalent JPG with no visible benefit, because PNG is lossless and photographs have no large flat areas for it to exploit.
Hitting a specific upload limit
Government forms, job applications and older web systems often impose limits like "under 2 MB" or "maximum 1024 Ã 1024". Work in this order:
- Check whether the limit is dimensions or file size. They are different constraints and need different fixes.
- Resize dimensions to the limit, or to about 1500 px if only file size is capped.
- Export as JPG at 80% quality. This is the sweet spot â visually indistinguishable from 100% at roughly a third of the size.
- If still too large, step quality down to 70%, then 60%. Below about 60% blocking artefacts become visible around edges and text.
- Convert HEIC to JPG if the upload is rejected outright rather than for size.
What actually destroys quality
- Repeated JPEG saves. Every save re-compresses. Editing and re-saving the same JPG ten times visibly degrades it. Keep an original and always export from that.
- Upscaling. Enlarging a 600 px image to 2000 px does not add detail; it interpolates, and the result looks soft and plasticky.
- Aggressive compression at full dimensions. A 4000 px image squeezed to 200 KB looks far worse than a 1200 px image at the same 200 KB.
- Screenshotting instead of exporting. A screenshot of a photo is limited to your screen resolution and adds a second round of compression.
Batch work
Resizing thirty photos one at a time is where people give up. Both a dedicated app and a browser tool handle batches: set the target width once, apply to the whole selection, export as a ZIP. If you are preparing images for a website or a listing, do the whole set at once so they are visually consistent.
