Common Aspect Ratios: 16:9, 4:3, 3:2, 1:1, 4:5, 21:9 and What They Are For

An aspect ratio is the shape of an image: width compared to height, written with a colon. A 16:9 video frame is 1.78 times wider than it is tall; a 4:5 portrait photo is narrower than it is tall (0.8). The ratio says nothing about size. A 1920×1080 wallpaper and a 3840×2160 video frame are both 16:9 — same shape, different detail.

Here is the catalogue you are probably looking for, followed by where each ratio actually shows up.

TOC

1. The common ratios at a glance

2. 16:9 — video and modern screens

3. 4:3 — the older screen shape

4. 3:2 — still photography

5. 1:1 — the square

6. 4:5 and 3:4 — portrait formats

7. 9:16 — full-screen phone video

8. 21:9 and other ultrawide numbers

9. 5:4 and 7:5 — the quiet standards

10. A-series paper — the √2 ratio

11. How to read any ratio yourself

The common ratios at a glance

Decimals are rounded to three places; each was checked by dividing the example dimensions (1920 ÷ 1080 = 1.7777…, 1080 ÷ 1350 = 0.8, 2560 ÷ 1080 = 2.3704…, and so on).

16:9 — video and modern screens

16:9 (1.778) is the frame shape of high-definition television. The ITU's Rec. 709, the standard behind HDTV, fixes the common image format at 1920×1080 pixels — 2,073,600 of them — at exactly 16:9. Its successor for ultra-HD, Rec. 2020, keeps the same shape at 3840×2160 and 7680×4320. Everything downstream inherits it: 720p (1280×720), 1080p, 4K, most TV panels, and a great many laptop screens.

For content, YouTube asks video thumbnails at 16:9 and recommends uploading them at 3840×2160 with a minimum width of 640 pixels. X's video specifications list 16:9 (and 1:1) as the recommended aspect ratios for uploads. When a platform "supports many ratios" it still tends to display 16:9 in its classic embeds and players.

4:3 — the older screen shape

4:3 (1.333) was the ratio of CRT televisions and the first generation of flat panels, and it survives in a few places with strong opinions behind them. Computer monitors of the era — VGA, SVGA, XGA — were all 4:3, so the first digital cameras matched them: most point-and-shoot cameras shoot 4:3, the Four Thirds and Micro Four Thirds systems are built around it, and Apple's iPad line kept the shape until the 11-inch iPad Pro moved to 1.43:1 in 2018. Silent-era 35 mm film was shot at 4:3 too, and Apple's iPhone camera guide still lists 4:3 alongside 16:9 and 1:1. A 4032×3024 photo checks out the same way: 4032 ÷ 3024 = 1.3333.

If an old photograph scans at 1024×768, that is 4:3. Print sizes are their own system: a 4×6-inch print is 3:2 (6 ÷ 4 = 1.5), so 35 mm and DSLR photos fill it exactly, while a 4:3 photo is cropped slightly top and bottom.

3:2 — still photography

3:2 (1.5) comes from 35 mm film: a 36×24 mm frame, which is 36 ÷ 24 = 1.5 exactly. Full-frame and APS-C digital sensors kept the family proportion, so a typical DSLR file of 3000×2000 pixels is 3:2. A handful of 2-in-1 laptops (Microsoft's Surface line among them) chose 3:2 for document work: taller screens fit more of a page.

3:2 and 4:3 are close enough that crops between them look mild, which is why photos "just get a little cut" in frames and feeds rather than failing to load.

1:1 — the square

1:1 is the neutral shape. Medium-format photographers used 6×6 cameras for it, platforms adopted it because it tiles well in grids, and profile pictures almost universally render square (they are then shown in a circle, which is a mask, not a different ratio). A 1080×1080 file has an aspect ratio of exactly 1:1 — width equals height, so 1080 ÷ 1080 = 1.

Instagram was built on it before adding taller formats; the square remains the one size every platform displays without negotiation.

4:5 and 3:4 — portrait formats

4:5 (0.8) is the standard portrait feed shape. Instagram's help documentation says feed photos keep their original resolution when their aspect ratio is between 1.91:1 and 3:4, and it spells the bound out in pixels: at a width of 1080, the height can be anything from 566 to 1440. So 1080×1350 (4:5) sits comfortably inside that range, and 1080×1440 (3:4, 0.75) is the tallest crop it preserves. Taller files get cropped.

Meta publishes a placement table showing which ratios each Facebook and Instagram ad placement accepts — 1.91:1, 16:9, 1:1, 4:5, 2:3 and 9:16 are the recurring column heads, with 9:16 marked "recommended for both images and videos" on the Stories and Reels rows. Portrait feed images exist because a phone is held upright: a 4:5 image occupies more of the screen than a 1:1 one.

On the film side, 4×5 large-format sheets give the ratio its other name; print it portrait and you have 4:5 (0.8), the same shape as the social feed portrait.

9:16 — full-screen phone video

9:16 (0.5625) is 16:9 stood on its end: 1080×1920, the resolution of full-screen vertical video. Instagram states that Reels accept aspect ratios from 1.91:1 up to 9:16, with a minimum resolution of 720 pixels and 30 fps. YouTube recommends 9:16 for Shorts thumbnails (2160×3840, minimum height 640 pixels). Pinterest recommends 9:16 or 1080×1920 for full-bleed video Pins.

Nothing here is universal — platforms also accept wider uploads and crop them — but 9:16 is the ratio designed for the phone held upright, and every vertical-video surface is built around it.

21:9 and other ultrawide numbers

"21:9" is a marketing name rather than a precise ratio. Written honestly, 21:9 = 7:3 = 2.333. The ultrawide monitors sold as 21:9 are usually something else: 2560×1080 is 64:27 (2.370) and 3440×1440 is 43:18 (2.389). Cinema's "Scope" convention is 2.39:1, which those panels approximate closely; the digital-cinema flat format is 1.85:1.

Use the label for the category (very wide screens, cinematic letterboxing), and the decimal for the math. If a spec sheet says 21:9, check the pixel dimensions before you compute a crop.

5:4 and 7:5 — the quiet standards

5:4 (1.25) shaped the SXGA era: 1280×1024 was the standard high-resolution LCD mode for years, and 5:4 is the shape of the 8×10-inch print (10 ÷ 8 = 1.25). 7:5 (1.4) is what you get from a 5×7 inch print held landscape: 7 inches wide, 5 inches tall (7 ÷ 5 = 1.4). Neither is fashionable, both still appear in frame shops, scanner presets and inherited monitor resolutions.

A-series paper — the √2 ratio

ISO 216 defines the A series: A0 down to A6, each size half the area of the next larger one. The trick is that halving preserves the shape, which requires a width:height ratio of √2 (about 1.414). A4 is 210×297 mm; 297 ÷ 210 = 1.4143, the ideal √2 = 1.4142 rounded to whole millimetres. Fold an A4 page in half and you get A5 with the same proportions — that is the property the ratio buys you.

The B series, also defined in ISO 216, follows the same logic. If you have ever wondered why an A4 page scaled up to A3 "just fits", the ratio is the reason: A3 is A4 with every dimension multiplied by √2 (210 × 1.414 ≈ 297).

How to read any ratio yourself

Two moves cover almost everything:

1. Get the decimal. Divide width by height. 1920 ÷ 1080 = 1.778 → 16:9 territory. 1080 ÷ 1350 = 0.8 → exactly 4:5.

2. Reduce the pair like a fraction. Divide both numbers by their greatest common divisor: 1920 and 1080 share 120, giving 16 and 9.

Sanity check: a decimal above 1 is landscape (width-led), below 1 is portrait (height-led), exactly 1 is square.

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