Your Thumbnails
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Real sizesWhat Survives Shrinking
How it worksA thumbnail is almost never seen at full size.
Three words, no more
Text on a thumbnail has to read at 160 pixels wide. Past three or four words it becomes a grey smear.
Readable at 160px
Contrast beats detail
Fine detail disappears first. What survives is the difference between light and dark, so build the image on that.
Squint test: still readable?
The corner is not yours
The duration badge sits bottom right and the progress bar runs along the bottom edge. Keep anything important out of both.
Bottom right = taken
Portrait crops cut the sides
Instagram now crops to 4:5, and reels covers to 9:16. Anything parked at the left or right edge of a 16:9 image simply will not appear.
16:9 → 4:5 loses 55%
Questions
03Is my image uploaded?
No. It is read into this page only, and it disappears when you reload.
What size should a thumbnail be?
1280 × 720 is the standard for YouTube. Anything larger is scaled down, anything smaller looks soft on desktop.
Why does the small one look different?
Downscaling averages neighbouring pixels, so thin lines and small text blur together. That is exactly what this tool is showing you.