Aspect ratio
Aspect ratio is the proportion of a video frame's width to its height, written as two numbers separated by a colon (16:9) or as a decimal (1.78:1). It describes shape, not size: 1280×720, 1920×1080 and 3840×2160 are all 16:9. Changing it after shooting means either cropping away picture or padding the frame with bars or a blurred backdrop. Most video today is delivered in four ratios: 16:9 for landscape, 9:16 for full-screen vertical, 4:5 for portrait feed posts and 1:1 for square.
Common Video Aspect Ratios
| Ratio | Decimal | Typical pixel sizes | Typical use |
|---|---|---|---|
| 16:9 | 1.78 | 1280×720, 1920×1080, 3840×2160 | YouTube, TV, webinars, screen recordings |
| 9:16 | 0.56 | 1080×1920, 2160×3840 | TikTok, Instagram Reels, YouTube Shorts, Stories |
| 1:1 | 1.00 | 1080×1080 | Square feed posts |
| 4:5 | 0.80 | 1080×1350 | Portrait posts in the Instagram and Facebook feeds |
| 4:3 | 1.33 | 640×480, 1440×1080 | Standard-definition TV and archive footage, phone photo sensors, a retro look |
| 21:9 / 2.39:1 | 2.33–2.39 | 2560×1080, 3440×1440, 2048×858 | Ultrawide monitors and the cinema “scope” look; letterboxed in standard players |
The colon and decimal forms mean the same thing: 16 ÷ 9 = 1.78. Cinema uses the decimal form with a trailing “:1” (1.85:1, 2.39:1) because those ratios don’t reduce to small whole numbers. The scope ratio has been 2.39:1 since SMPTE revised the anamorphic standard in 1970; “2.35” survives as a name for the look.
16:9 is a deliberate compromise. In the 1980s Kerns H. Powers, working in SMPTE’s high-definition group, showed that a 1.78 frame sits close to the geometric mean of 4:3 and scope (√(1.33 × 2.39) ≈ 1.78), so both fit inside it with the least waste. It became the HDTV standard.
Aspect Ratio vs. Resolution
Resolution is how many pixels a frame has; aspect ratio is the shape they form. 1280×720, 1920×1080 and 3840×2160 differ ninefold in pixel count and are all 16:9. You can change one without the other, and the costs differ: changing resolution changes how finely the picture is sampled, while changing aspect ratio changes what is inside the frame. “1080p” usually implies 16:9, but a 1080×1920 vertical video is 1080p too.
How to Convert Between Aspect Ratios
There are two ways to change a frame’s shape, and one number tells you what each costs: divide the smaller ratio by the larger one. Going from 16:9 (1.78) to 9:16 (0.5625) gives 0.316.
- Crop keeps that share of the picture and fills the new frame. To crop to a narrower ratio, keep the full height and take a window as wide as height × target ratio: 1080 × 9/16 = 607.5, so 608 pixels.
- Fit (pad) keeps the whole picture, and it fills that share of the new frame. The rest is black bars or a blurred copy of the picture.
| Conversion | Crop keeps | Crop window | Fit result |
|---|---|---|---|
| 16:9 → 9:16 | 31.6% of the width | 608×1080 of 1920×1080 | 1080×608 picture in a 1080×1920 frame |
| 16:9 → 4:5 | 45% of the width | 864×1080 of 1920×1080 | 1080×608 picture in a 1080×1350 frame |
| 16:9 → 1:1 | 56.25% of the width | 1080×1080 of 1920×1080 | 1080×608 picture in a 1080×1080 frame |
| 9:16 → 16:9 | 31.6% of the height | 1080×608 of 1080×1920 | 608×1080 picture in a 1920×1080 frame |
| 4:3 → 16:9 | 75% of the height | 1440×810 of 1440×1080 | 1440×1080 picture in a 1920×1080 frame |
| 2.39:1 → 16:9 | 74% of the width | 1525×858 of 2048×858 | 1920×803 picture in a 1920×1080 frame |
A crop is then scaled to the output size, which enlarges it: the 608×1080 window becomes 1080×1920 and holds no more detail than before. From a 4K source the 9:16 window is 1215×2160, so shoot 4K when you’ll cut verticals. Which method to use depends on the shot: crop a talking head, fit gameplay, slides and screen recordings. Choosing that shot by shot is what auto reframe automates, and the aspect ratio calculator works out exact dimensions.
Pixel Aspect Ratio
Pixels are not always square. Three quantities are related by one identity:
SAR (stored pixels, w:h) × PAR (shape of one pixel) = DAR (what you see)
In modern square-pixel video PAR is 1, so the stored size and the displayed shape match. Older formats store the picture squeezed: HDV stores 1440×1080 with a PAR of 4:3 and displays as 16:9, and widescreen PAL DVD stores 720×576 with a PAR of 64:45 (1.25 × 1.42 ≈ 1.78). Software that reads the stored pixels and ignores the PAR flag is why older footage sometimes exports stretched or squashed.
Aspect Ratios by Platform
TikTok, Instagram Reels and YouTube Shorts are 9:16 at 1080×1920. Instagram feed posts use 4:5 or 1:1, and standard YouTube is 16:9. The full table, with links to each platform’s spec page, is on resize video for TikTok, Instagram and YouTube. Vertical apps also draw their own interface (username, caption, buttons) over the bottom and right edge of the picture, so keep text away from those edges.
How Valmera Handles Aspect Ratio
In Valmera you ask for 9:16, 1:1, 4:5, 16:9 or the source ratio in plain English. The agent crops (aimed at the subject), pads with bars or fits over a blurred backdrop, and in auto mode it decides per camera shot (see auto reframe). To change the shape for one section and back, including to 4:3, use an aspect shift. Exports keep the source’s short side, so a 1080p source exports at 1080×1920 for 9:16.
Frequently Asked Questions
Made with Valmera: real exports
Change the Aspect Ratio by Describing It
Upload a video, ask for 9:16, 1:1 or 4:5, and the agent crops or fits each shot. Creating an account and uploading are free. Editing requires a subscription.
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