How aspect ratios work
An aspect ratio is the shape of the picture: its width divided by its height. It is written either as two whole numbers (16:9, 4:3, 9:16) or as a decimal against 1 (1.85:1, 2.39:1). Both mean the same thing: 16:9 is 1.78:1. The ratio says nothing about resolution: 1280×720, 1920×1080 and 3840×2160 are all 16:9.
Choosing a ratio is a creative decision as much as a technical one. A wide 2.39:1 frame puts people in their surroundings and suits landscapes, groups and spectacle. A squarer 4:3 or 1.85:1 frame brings faces closer and feels more intimate. Vertical 9:16 is built for phones: one subject, centred, close.
Letterboxing, pillarboxing and cropping
When a picture's shape doesn't match the screen, you either add black bars or crop. A picture wider than the frame gets bars top and bottom (letterbox); a narrower one gets bars at the sides (pillarbox). Cropping fills the frame but throws part of the picture away, which is why the calculator shows how much you'd lose. If you plan to deliver several shapes, frame important action inside the area they all share.
Common ratios
- 16:9 (1.78:1): HD and 4K television, YouTube and most streaming.
- 1.85:1: theatrical "flat" widescreen, close to 16:9.
- 2.39:1: anamorphic "scope" widescreen, still often called 2.35 or 2.40.
- 4:3 (1.33:1): standard-definition TV and the classic academy look, popular again for period and intimate films.
- 9:16: vertical video for TikTok, Instagram Reels and YouTube Shorts (1080×1920).
- 4:5 and 1:1: Instagram's portrait and square feed posts.
Where to go next
The course lesson Export and delivery covers delivering one film in several shapes, and Short-form vertical covers framing for phones. To plan frames in your chosen shape, print a storyboard template in that ratio, and use the file size calculator to check the export will fit.