Social media video size is two numbers pretending to be one: the aspect ratio defines the shape of the frame (9:16, 4:5, 1:1, 16:9), and the resolution defines how many pixels fill that shape (1080 by 1920, 1080 by 1350, and so on). Most sizing confusion dissolves the moment those two are separated.
The rule that this whole series serves: choose the aspect ratio for the viewing experience, then compose every important visual element for the space that remains visible. A technically accepted format is not a well-composed one; interface buttons, captions and cropping can still swallow the part of the frame that mattered.
One honest warning before any table of numbers: platform specifications change. Every platform page in this series carries its verification date (July 29, 2026) and the same advice: check the current official requirements before an important campaign. Accepted, recommended and required are three different words, and treating them as synonyms is how videos get cropped.
Seven guides: the 9:16 ratio itself, the exact numbers for TikTok, Instagram Reels, YouTube Shorts and LinkedIn, vertical dimensions beyond 9:16, and the safe zones that keep your captions out from under the interface.