There is one right answer here and a lot of folklore, so it is worth stating plainly.
The number
| Value | Why | |
|---|---|---|
| Resolution | 1080 × 1920 | Native on every vertical surface |
| Aspect ratio | 9:16 | The full phone screen |
| Container | MP4 (H.264) | Universally accepted |
| Frame rate | 30 fps | Matches most phone footage |
| Audio | AAC, 44.1 kHz | Standard for every platform |
Every platform re-encodes on upload and downsamples to 1080×1920, so a bigger file is never shown bigger. A clean 2K master (1440×2560) can still come out slightly sharper, because the platform's own downscale has more detail to work from; past that, a larger file only adds upload time. Going below 1080×1920 is visible immediately, particularly on text.
The safe area
The video fills the screen, but the interface is drawn on top of it. Anything you place in those regions is covered by a caption, a username, a follow button or a row of icons.
- Top ~250 px: status bar and the platform's own header.
- Bottom ~420 px: caption, handle, audio strip, action buttons.
- Right ~180 px: the vertical column of like, comment and share.
What about square and 4:5?
Those are feed formats, not reel formats. A 4:5 image post takes more of the feed than a square one, which is why carousels use it. But a vertical video posted at 4:5 is letterboxed on a reels surface, wasting a third of the screen.
If a piece of content has to be both, render it twice rather than compromising on one file that suits neither.
Getting it right without thinking about it
Easy Reels renders at 1440×2560 by default, a 9:16 vertical 2K master that each platform downsizes to its own 1080×1920, and positions reusable text overlays with the safe area already in mind, so a handle placed once sits correctly on every video you make afterwards.