Pixel dimensions and compression determine most image file sizes. Working in that order usually gets an image under an upload or email limit without visible damage at its intended display size.
Start with the dimensions
A modern phone photo is around 4,000 × 3,000 pixels. An email or listing may display only a small fraction of those pixels. Resizing the photo before upload removes data the destination would discard.
Resizing is the single most effective way to shrink a file, because size scales with pixel count. Halving the width and height cuts the pixel count; and roughly the file size; by 75%. For anything viewed on a screen, 1,500–2,000 pixels on the long edge is plenty. For a small web thumbnail, 400–800 pixels is enough.
Don't downsize your only copy if you may print it or crop it again later. Deleted pixels can't be recovered. I keep the camera original and make a smaller copy for the upload.
Then set the compression
JPG and WebP quality settings usually run from 0–100. The scale is not linear:
- 100 to ~85: the file often shrinks by half or more with little visible change.
- ~85 to ~70: more meaningful savings; artifacts start to appear in smooth gradients like skies if you zoom in.
- below ~60: diminishing returns and visible damage; blockiness, smeared detail, halos around edges.
I normally start around quality 82 for photos, then look at the preview rather than trusting the number. Quality 100 rarely earns its extra file size. A smooth sky or text near a hard edge will show compression trouble before most of the picture does.
The order matters: resize first, then compress
Crop first, resize to the displayed dimensions, then apply compression. A photo reduced to a quarter of its original pixel count and saved near quality 82 can be 90–95% smaller without a visible change at its display size.
Check the format before anything else
A large file may be a photo saved as PNG. Converting it to JPG or WebP can reduce the size by 80% before you change the quality setting. Screenshots and diagrams often stay clearer as PNG. The format guide covers the differences.
Some useful starting points
- Email attachment: aim under 1–2 MB per photo. Resize to ~1,600 px long edge, JPG quality ~80.
- Website images: aim under 200–300 KB. Resize to the displayed size (or 2× for sharp high-DPI screens), WebP if you control the site.
- Form uploads with hard limits: resize first; only lower quality below ~75 if you still miss the limit.
- Profile pictures: most platforms display them tiny; 500–800 px square at quality 80 is more than enough.
Doing it in your browser
The resize & compress tool handles this workflow in your browser. Set a percentage or exact dimensions, choose JPG or WebP, check the preview, then download. Start with the crop tool when edges need trimming.