3:1 aspect ratio
3:1 is the wide header shape: 3 units wide for every 1 tall, which is 3 as a decimal. 1500 x 500 px is 3:1 because 1500 divided by 500 gives 3, and the fraction reduces to 3:1. 2 of the image sizes on this site use it.
Where 3:1 comes from
3:1 is a header band rather than an image. It exists because a profile page needs a strip across the top that stays a strip at any window width, with a profile picture overlapping it.
Which platforms use 3:1
Read live from the specification data, so this list changes when a platform does. Last verified 2026-07-27.
| Platform | Asset | Size (px) | Source |
|---|---|---|---|
| X (Twitter) | Header | 1500 x 500 | Convention |
| Bluesky | Banner | 1500 x 500 | Convention |
3:1 in pixels
Every row below is calculated from the ratio rather than looked up, so the heights are exact where the arithmetic is exact and rounded to the nearest whole pixel where it is not. A fractional pixel is not something a file can store.
| Width | Height | Used by |
|---|---|---|
| 1080 px | 360 px | - |
| 1200 px | 400 px | - |
| 1500 px | 500 px | X (Twitter) header, Bluesky banner |
| 1920 px | 640 px | - |
Cropping and letterboxing into 3:1
Almost nothing photographic survives a 3:1 crop with its subject intact. Design for the shape instead: keep the meaningful content centred and treat the far edges as expendable, because responsive layouts trim them.
There are only two honest ways to put an image of one shape into a frame of another. Crop to fill keeps the frame full and throws away whatever does not fit, which is almost always what you want for a feed. Fit inside keeps the whole image and pads the remaining space, which is what you want when the image is a diagram, a screenshot or anything where losing an edge loses meaning. Scaling to fit without doing either, so the image is stretched, is the one option that is always wrong.
Work out a 3:1 size
Enter a width or a height and the calculator solves the other side. It runs in your browser and nothing is uploaded.
Other ratios
See the aspect ratio guide for the shapes side by side, or the full cheat sheet for every size on one page.