Why photos are big: pixels times detail
Uncompressed, a 12 megapixel photo is about 36 MB (12 million pixels, 3 bytes each). The JPEG your phone saved is commonly 2 to 5 MB because compression drops detail the eye barely notices.
Both numbers grow with the pixel count, which makes dimensions the first thing to check.
Step 1: reduce the dimensions to what you display
Halving the width and height cuts the pixel count by 75 percent, and the file usually shrinks by roughly that much. No quality slider gets you a saving that large without visible damage.
| Use | Longest side | Compress preset |
|---|---|---|
| Full-width website banner | 1920 px | Web 1920 |
| Email attachment | 1280 px | Email 1280 |
| Blog post or profile picture | 800 to 1200 px | Small 800 |
Step 2: lower the quality until you can see the difference
JPEG and WebP quality trades detail for bytes. The Compress tool starts at 75 and stops at 30. For photos, 70 to 85 usually looks the same at normal viewing size. Below roughly 50, blocky artifacts start to show in skies and skin.
Check at 100% zoom, not fit-to-screen. Faces, text and smooth gradients show damage first.
Step 3: choose a format that suits the picture
Photos compress best as JPEG or WebP. The same photo saved as PNG is commonly several times larger, because PNG is lossless. PNG earns its size on screenshots, logos and anything with transparency.
Google's published comparison found lossy WebP files 25 to 34 percent smaller than JPEG at equal visual quality. Results vary with the photo, so compare both on your own image before committing.
Compress once, from the original
Each lossy save re-quantizes the picture and adds artifacts. Keep your original and export a fresh copy every time instead of recompressing a copy of a copy.
Check the size before you download
The Compress tool shows the original and the new file size as you adjust, with the percentage saved. Change one setting at a time (dimensions first) so you know which one bought the saving, and stop when the file is small enough for the place it is going.
