Glossary
What is the rule of thirds?
By the KeyMo team · Updated
The rule of thirds is a framing guide. Two vertical and two horizontal lines divide the picture into nine equal boxes, and the subject sits on a line or where two lines cross instead of dead centre. In a 9:16 clip, that usually means a speaker's eyes land near the upper horizontal line.
The rule of thirds, defined
Draw two evenly spaced vertical lines and two evenly spaced horizontal lines across a picture. You get a 3 by 3 grid. The rule of thirds says the strongest places for a subject are on those lines, and the strongest of all are the four points where they cross. The same definition applies in photography, film, cinematography, painting and graphic design, which is why the phrase shows up with so many different endings in search.
It is a guideline, not a law. It exists because a subject placed exactly in the middle of a frame tends to look static, while a slightly offset subject gives the picture some tension and room to breathe. Plenty of good shots ignore it on purpose.
The grid on a 1080x1920 clip
KeyMo clips are 9:16 at 1080x1920. Divide each side by three and you get the numbers below, counted from the top left corner of the frame.
| Line | Position in pixels | Use it for |
|---|---|---|
| Left vertical | x = 360 | Holding a speaker who looks to the right |
| Right vertical | x = 720 | Holding a speaker who looks to the left |
| Upper horizontal | y = 640 | Eye line of a head-and-shoulders shot |
| Lower horizontal | y = 1280 | Hands, a prop, or the base of a caption block |
On a tall frame the upper line does most of the work. Put the eyes on it and the face sits comfortably in the top half, with the shoulders and chest filling the space below.
Where the rule of thirds meets the safe zone
Vertical feeds cover parts of your picture with buttons, names and captions, which is why a clean grid is not the whole story. For its Reels ads, Meta asks advertisers to keep roughly 14% of the top, 35% of the bottom and 6% of each side free of text, logos and key elements. On a 1080x1920 frame, 35% of the height is 672 pixels, so the covered strip starts near y = 1248. The lower third line at y = 1280 is already inside it. That guidance is written for ads, so treat it as a cautious reference for normal posts, not a measured rule.
Practical result: the upper line is a safe home for a face, while the lower line is a bad place for anything you need people to read. See safe zone for the longer version.
Worked example: one speaker, then two
A host talks to camera in a 16:9 recording and is cut to 9:16. The face sits in the middle of the wide frame, so a straight crop centres it. Nudge the crop so the eyes land on y = 640 and the picture feels less like a webcam call.
- Looking straight at camera: centre or slightly off-centre is fine, with the eyes on the upper line.
- Looking to one side: put the speaker on the opposite vertical line so there is space in front of the face. That space is called lead room.
- Two people in one wide frame: do not squeeze both onto the lines. Cut to whoever is speaking, or look at a split screen layout.
Common mistakes
- Treating the grid as a cage. If a centred face looks right, leave it.
- Putting the eyes on the line and then cutting off the top of the head. Check headroom as well.
- Framing for the grid and forgetting that a caption block will sit on top of the lower third.
- Moving the crop every few seconds. A steady frame beats a perfectly placed one that drifts.
Where KeyMo fits
KeyMo turns a horizontal recording into vertical clips and follows the face with automatic face-tracking reframe. It does not ask you to draw a grid. If a clip is framed in a way you dislike, you can open it in the chat editor and tell KeyMo what to change, then check the result on your phone. See auto reframe and face tracking for how that works in general.
Sources: Meta: safe zone for 9:16 ads (checked 11 October 2026); Meta Ads Guide: Instagram Reels video ads (checked 11 October 2026).