Video aspect ratios explained: 16:9, 9:16, 4:3, 1:1 and 2.39:1 with their pixel sizes
An aspect ratio is the shape of the frame: its width divided by its height. 16:9 is the widescreen rectangle every television, YouTube player and laptop uses; 9:16 is that same rectangle turned upright for phones; 4:3 is the older, squarer television and photography frame; 1:1 is a square; and 2.39:1 is the very wide cinema frame. The ratio says nothing about resolution. A 16:9 frame can be 640 x 360 or 3840 x 2160, and both are exactly the same shape. This guide gives every common ratio its pixel sizes, says which platform expects which, and shows how to move a clip between them without stretching anyone's face.
What does an aspect ratio actually mean?
An aspect ratio is width to height, written as two numbers with a colon: 16:9 means the frame is 16 units wide for every 9 units tall, so 1920 x 1080, 1280 x 720 and 3840 x 2160 are all 16:9 because each divides to 1.78.
The arithmetic is the whole concept. Divide width by height and you get a single number: 16 divided by 9 is 1.78, 4 divided by 3 is 1.33, 9 divided by 16 is 0.56. Two frames with the same result have the same shape regardless of size. That is why resolution and aspect ratio are separate settings in every editor, and why "1080p" tells you the height but not the shape: 1080p is 1920 x 1080 at 16:9, but a 1080p vertical video is 1080 x 1920.
Which aspect ratio is which, in pixels?
| Ratio | Decimal | Common pixel sizes | Where you meet it |
|---|---|---|---|
| 16:9 | 1.78 | 1280 x 720, 1920 x 1080, 2560 x 1440, 3840 x 2160 | YouTube, televisions, laptops, most cameras |
| 9:16 | 0.56 | 1080 x 1920, 720 x 1280, 2160 x 3840 | Reels, Shorts, TikTok, Stories, phone screens |
| 4:3 | 1.33 | 640 x 480, 1024 x 768, 1440 x 1080, 1600 x 1200 | Older television, iPad screens, classic photography |
| 1:1 | 1.00 | 1080 x 1080, 1200 x 1200, 3000 x 3000 | Square social posts, album covers, profile images |
| 4:5 | 0.80 | 1080 x 1350 | Portrait feed posts on Instagram |
| 3:4 | 0.75 | 1080 x 1440 | The tallest photo ratio Instagram keeps uncropped, per its help centre in September 2026 |
| 1.85:1 | 1.85 | 1920 x 1038, 4096 x 2214 | "Flat" cinema, the narrower of the two theatrical standards |
| 2.39:1 | 2.39 | 1920 x 803, 2048 x 858, 4096 x 1716 | "Scope" widescreen cinema, often called cinemascope or anamorphic |
| 21:9 | 2.33 to 2.37 | 2560 x 1080, 3440 x 1440 | Ultrawide monitors; a marketing label, not a single exact ratio |
Two of those need a note. "21:9" monitors are actually 2.33:1 or 2.37:1 depending on the panel, which is why a true 2.39:1 film still shows thin bars on an ultrawide screen. And 4:5 versus 3:4 matters on Instagram: 4:5 (1080 x 1350) was the tallest feed ratio for years, and Instagram's photo help page now states it keeps photos uncropped between 1.91:1 and 3:4, so 1080 x 1440 is the new tallest safe frame (help.instagram.com, checked September 2026).
What is the 16:9 aspect ratio?
16:9 is the widescreen standard: 1920 x 1080 (Full HD), 1280 x 720 (HD), 2560 x 1440 (QHD) and 3840 x 2160 (4K UHD) are all 16:9. It is the native shape of YouTube's player, of every modern television and of nearly every laptop and monitor, which is why a 16:9 export needs no letterboxing anywhere on the desktop web. If a resolution divides to 1.78 it is 16:9; the aspect ratio calculator does the division and returns the missing side for any width or height you type.
What is the 9:16 aspect ratio?
9:16 is 16:9 rotated: 1080 x 1920 is the standard, 720 x 1280 the minimum most platforms accept, and 2160 x 3840 the 4K version. It exists because phones are held upright, and the vertical feeds (Reels, Shorts, TikTok, Stories) fill the whole screen only with a 9:16 clip. Instagram states reels may be uploaded between 1.91:1 and 9:16 with a minimum of 720 pixels of resolution and 30 frames per second (Instagram Help, checked September 2026), and YouTube caps Shorts uploads at 1080p (YouTube Help, checked September 2026). The vertical frame has its own composition rules, covered in the vertical video guide.
What is the 4:3 aspect ratio?
4:3 is the pre-widescreen television and computer-monitor shape: 640 x 480, 800 x 600, 1024 x 768 and 1440 x 1080. It survives in iPad screens, in archival footage, in a lot of classic photography and in retro-styled edits that letterbox 4:3 inside a 16:9 frame on purpose. Converting old 4:3 material to a modern 16:9 export is the most common aspect-ratio job in editing, and the honest answer is that you either crop the top and bottom, pad the sides, or accept a stretched image; there is no fourth option.
What is a cinematic aspect ratio?
Cinema uses two frames: 1.85:1 ("flat") and 2.39:1 ("scope", the widescreen bars people call cinematic); a 16:9 video gets the scope look by masking the top and bottom of the frame to 2.39:1, which costs about 25% of the picture height.
Masking is not the same as shooting wide. A 1920 x 1080 frame masked to 2.39:1 keeps 1920 x 803 pixels of picture; the bars are just black pixels added to fill a 16:9 container. It reads as cinematic because audiences associate the shape with theatrical film, and it works best with wide shots and slow camera moves, which is also how AI-generated footage tends to look its best. If you generate 16:9 clips and mask them, frame the subject in the middle 75% of the height so the mask never cuts a head.
Which aspect ratio should you shoot or generate in?
Generate in the ratio of the destination, then derive the others by cropping, never by stretching:
- YouTube, web embeds, presentations: 16:9.
- Reels, Shorts, TikTok, Stories: 9:16.
- Instagram feed and carousels: 4:5 or 3:4, with 1:1 as the safe fallback.
- Cinematic short films and trailers: 16:9 delivered, masked to 2.39:1 in the edit.
PrismPoster's Video Studio renders in 16:9 and 9:16, so a piece that needs both a widescreen cut and a vertical cut is two generations, not one generation cropped. Set the ratio in the composer before writing the prompt: the model composes for the frame it is given, and a horizontal scene cropped to vertical loses the sides where the action usually is. Image inputs get the same treatment with the free crop image for video tool, which shows exactly what a 16:9 or 9:16 crop removes before you commit it.
How do you convert between aspect ratios without stretching?
There are three honest methods and one dishonest one:
- Crop. Keep the height, cut the sides (16:9 to 9:16 loses 68% of the width) or keep the width and cut the top and bottom (4:3 to 16:9). Best when the subject sits in the middle.
- Pad. Keep the whole picture and fill the empty area with black bars, a blurred copy of the frame, or a solid brand colour. Best for archival footage and anything with text at the edges.
- Reframe. Re-shoot or regenerate in the target ratio. Best quality, and with AI video the cheapest, because a second generation costs credits rather than a crew.
- Stretch. Scale the width and height by different amounts. Never do this; it distorts faces and text and every viewer notices.
The aspect ratio resizer and safe-zone preview previews crop and pad across 16:9, 9:16, 1:1 and 4:5 with the platform overlays drawn in, and the social media sizes reference lists the pixel target for each placement so you export once at the right size. Resolution decisions, which are a separate question from ratio, are in AI video resolutions explained.
Frequently Asked Questions
Is 1920 x 1080 a 16:9 aspect ratio?
Yes. 1920 divided by 1080 is 1.78, the same as 16 divided by 9. So are 1280 x 720, 2560 x 1440 and 3840 x 2160; they differ in resolution, not in shape.
What resolution is a 4:3 aspect ratio?
Any size where width divided by height equals 1.33: 640 x 480, 800 x 600, 1024 x 768, 1440 x 1080 and 1600 x 1200 are the common ones. 1440 x 1080 is the usual choice when 4:3 footage has to sit inside a Full HD timeline.
What is the difference between 4:5 and 3:4?
Both are portrait ratios for feed photos. 4:5 is 1080 x 1350 and was Instagram's tallest supported feed ratio for years; 3:4 is 1080 x 1440, slightly taller, and Instagram's help centre states in September 2026 that photos between 1.91:1 and 3:4 are kept at their original ratio. Use 3:4 when you want the most screen height in the feed.
What aspect ratio do AI video generators use?
Most, including PrismPoster's Video Studio, generate 16:9 and 9:16, with clips of 4, 6, 8, 10 seconds. A square or 4:5 social cut is made by cropping a 9:16 or 16:9 generation in the editor, not by generating at that ratio.
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