Last reviewed on 2026-05-02.
What an aspect ratio is
An aspect ratio is the relationship between the width and height of a rectangle, written as width:height. It is not a size. A 32-inch TV and a 65-inch TV can both have a 16:9 ratio; only the absolute dimensions differ. Two displays with the same diagonal but different ratios will have very different widths and heights.
Knowing the diagonal alone is rarely enough. To compare a 27-inch 16:9 monitor to a 34-inch 21:9 ultrawide, the ratio decides which one shows two browser windows side-by-side comfortably and which one feels taller for word-processing.
Quick answer: 16:9 is the most common aspect ratio in use today — a decimal ratio of 1.78, meaning the screen is 1.78 times wider than it is tall. It covers virtually every television, 1080p and 4K video, and most laptops. 4:3 (1.33) is the older, squarer television and iPad ratio; 21:9 (2.33) is the ultrawide and cinematic ratio.
Common aspect ratios at a glance
| Ratio | Decimal | Where you see it | Quick note |
|---|---|---|---|
| 16:9 | 1.78 | HDTV, most laptops, YouTube video | The default modern screen ratio |
| 16:10 | 1.60 | Many laptop and tablet screens | Slightly taller than 16:9; more vertical room |
| 21:9 (2.39:1) | 2.33 | Ultrawide monitors, cinematic film | Roughly two 8.5:9 panels side by side |
| 32:9 | 3.56 | Super-ultrawide gaming monitors | Two 16:9 panels stitched together |
| 4:3 | 1.33 | Older TVs, classic photos, iPad | Square-leaning; common for documents |
| 3:2 | 1.50 | 35 mm photos, some laptops | The DSLR / mirrorless default |
| 5:4 | 1.25 | Older 17" and 19" monitors | Almost square; rarely sold today |
| 1:1 | 1.00 | Instagram square posts, vinyl covers | Identical width and height |
| 9:16 | 0.56 | Phone video, TikTok, Stories, Reels | Vertical sibling of 16:9 |
| 4:5 | 0.80 | Instagram portrait posts | The tallest format Instagram allows in-feed |
| 2:3 | 0.67 | Pinterest pins, vertical 35 mm prints | Vertical sibling of 3:2 |
| √2 : 1 | 1.414 | ISO paper (A4, A3) | The only ratio that halves to itself |
Aspect ratio by resolution
A resolution is a pixel count; the aspect ratio is what that count simplifies to. Divide the width by the height, or reduce both numbers by their greatest common divisor, and you have the ratio. These are the resolutions you are most likely to meet.
| Resolution | Common name | Aspect ratio | Decimal |
|---|---|---|---|
| 1280 × 720 | 720p / HD | 16:9 | 1.78 |
| 1920 × 1080 | 1080p / Full HD | 16:9 | 1.78 |
| 2560 × 1440 | 1440p / QHD | 16:9 | 1.78 |
| 3840 × 2160 | 4K UHD | 16:9 | 1.78 |
| 7680 × 4320 | 8K UHD | 16:9 | 1.78 |
| 1366 × 768 | Budget laptop HD | ~16:9 | 1.78 |
| 1920 × 1200 | WUXGA | 16:10 | 1.60 |
| 2560 × 1600 | WQXGA | 16:10 | 1.60 |
| 2880 × 1800 | MacBook Pro Retina | 16:10 | 1.60 |
| 2560 × 1080 | UW-FHD ultrawide | 21:9 | 2.37 |
| 3440 × 1440 | UW-QHD ultrawide | 21:9 | 2.39 |
| 5120 × 1440 | Super ultrawide | 32:9 | 3.56 |
| 1024 × 768 | XGA | 4:3 | 1.33 |
| 2048 × 1536 | iPad Retina | 4:3 | 1.33 |
| 3000 × 2000 | Surface Laptop | 3:2 | 1.50 |
| 1080 × 1920 | Vertical 1080p | 9:16 | 0.56 |
Two entries deserve a note. 1366 × 768 divides to 1.779, not exactly 1.778 — it is marketed as 16:9 and behaves as 16:9, but the pixel grid is a rounding of it. 21:9 is a marketing label rather than a true ratio: 2560 × 1080 is actually 64:27 (2.37) and 3440 × 1440 is 43:18 (2.39). Both are close enough to the 2.39:1 cinema standard that a widescreen film fills the panel edge to edge.
How to calculate an aspect ratio
Divide both pixel dimensions by their greatest common divisor. For 1920 × 1080, the greatest common divisor is 120: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, giving 16:9. For 2048 × 1536 the divisor is 512, giving 4:3.
To find a missing dimension at a fixed ratio, multiply or divide by the decimal. A 16:9 image 1500 px wide needs a height of 1500 ÷ 1.78 = 843 px. A 4:5 Instagram portrait 1080 px wide needs 1080 ÷ 0.80 = 1350 px tall. Going the other way, a 9:16 vertical video 1920 px tall is 1920 × 0.56 = 1080 px wide.
For screens the useful calculation is different, because you are given a diagonal rather than a width. For a 16:9 panel, width = diagonal × 0.872 and height = diagonal × 0.490. A 55-inch television is therefore 47.9 inches wide and 27.0 inches tall — the numbers in the table below.
16:9 screen dimensions by diagonal
Screen width and height for every common diagonal at a 16:9 ratio, in inches and centimetres. These are screen-area figures; the physical cabinet or bezel adds roughly half an inch on each side.
| Diagonal | Width | Height | Metric (W × H) | Full guide |
|---|---|---|---|---|
| 24 in | 20.9 in | 11.8 in | 53.1 × 29.9 cm | 24 inch monitor dimensions |
| 27 in | 23.5 in | 13.2 in | 59.8 × 33.6 cm | 27 inch monitor dimensions |
| 32 in | 27.9 in | 15.7 in | 70.8 × 39.8 cm | 32 inch TV dimensions |
| 43 in | 37.5 in | 21.1 in | 95.2 × 53.5 cm | 43 inch TV dimensions |
| 50 in | 43.6 in | 24.5 in | 110.7 × 62.3 cm | 50 inch TV dimensions |
| 55 in | 47.9 in | 27.0 in | 121.8 × 68.5 cm | 55 inch TV dimensions |
| 65 in | 56.7 in | 31.9 in | 143.9 × 80.9 cm | 65 inch TV dimensions |
| 75 in | 65.4 in | 36.8 in | 166.0 × 93.4 cm | 75 inch TV dimensions |
| 85 in | 74.1 in | 41.7 in | 188.2 × 105.8 cm | 85 inch TV dimensions |
Because every one of these is 16:9, they are all the same shape — only the scale changes. That is also why screen area grows far faster than the diagonal suggests: an 85-inch panel has 2.4 times the area of a 55-inch one, not 1.5 times, because area scales with the square of the diagonal. The full range is in the TV sizes guide and the monitor sizes guide.
How TVs, monitors, and phones use ratios
Almost every modern television is 16:9. Phone screens were 16:9 for years and are now mostly between 19.5:9 and 20:9 (taller). Tablets are split: iPads use 4:3 across most sizes, while many Android tablets use 16:10. Most laptops use 16:9 or 16:10, with a small but growing share of 3:2 (popular in the Microsoft Surface line and several premium laptops).
Monitors are where the ratio actually changes the day-to-day experience. A 27-inch 16:9 monitor and a 34-inch 21:9 ultrawide have similar physical heights, so the ultrawide does not feel taller; it adds horizontal space, which is why it is often described as a "two windows side by side" monitor rather than a "bigger" one.
How film and video use ratios
Cinema uses wider ratios than broadcast. A typical theatrical film is shot in 1.85:1 or 2.39:1. When that 2.39:1 image plays on a 16:9 TV, the result is letterboxing — black bars on the top and bottom — because the film image is wider relative to its height than the TV's frame. The same effect, in reverse, happens when a 4:3 archival show plays on a 16:9 TV: pillarboxing on the sides.
Streaming services and modern broadcast television default to 16:9. Vertical video for phones is 9:16, with platforms increasingly designing for that ratio first — full-screen Stories, Reels, and Shorts all expect a 9:16 source.
How photo and print use ratios
Most cameras capture in 3:2 (full-frame and APS-C sensors) or 4:3 (Micro Four Thirds and most phone cameras). When you order a print at a non-matching ratio, something has to give. A 3:2 photo printed at 8×10 inches (effectively a 4:5 ratio) loses a strip from one or both ends. A 4:3 photo printed at 4×6 inches (a 3:2 frame) has the same problem in the opposite direction. Picking a print size that matches the capture ratio is the only way to keep the entire frame.
Paper sizes follow a different logic. ISO 216 paper (A4, A3, A5, and so on) uses a √2:1 ratio specifically because it is the only ratio that, when folded in half, produces a smaller rectangle with the same proportions. That is why two A5 sheets fit perfectly inside one A4 sheet without trimming. ANSI Letter (8.5×11 inches) is roughly 1.29:1 — close to 4:3 but not identical.
Comparing two ratios that look similar
Pairs like 16:9 and 16:10, or 3:2 and 4:3, look close but feel different in practice. Two checks help:
- Convert to a decimal. 16:9 is 1.78, 16:10 is 1.60. The ratio with the higher decimal is wider. The lower decimal is taller.
- Hold the diagonal constant. A 24-inch 16:9 monitor is about 20.9×11.8 inches. A 24-inch 16:10 monitor is about 20.4×12.7 inches — almost an inch shorter on width but nearly an inch taller on height. The "more vertical room" advantage of 16:10 is concentrated in that extra inch.
The same logic explains why 21:9 ultrawides at 34 inches feel similar in height to a 27-inch 16:9 monitor: their diagonals differ, but their heights are close because the ultrawide spends most of its diagonal on horizontal extent.
Ratios for social and product images
Each social platform expects a specific ratio for each placement. Instagram in-feed accepts 1:1, 4:5, and 1.91:1; Stories and Reels are 9:16. Facebook feed is 1.91:1 for link previews and 4:5 for portrait posts. YouTube thumbnails and video are 16:9. Pinterest pins favor 2:3 vertical. Designing one image at the platform's preferred ratio almost always looks better than scaling a 16:9 image and accepting cropping.
Common mistakes
- Treating diagonal as the only number that matters. Two screens with the same diagonal can have very different widths.
- Mixing capture and print ratios without cropping in the editor. Letting the print shop crop usually removes important parts of the frame; cropping yourself preserves what matters.
- Forgetting that 4:3 and 3:4 are the same ratio rotated. Some platforms list both forms; the only difference is orientation.
- Confusing pixel ratio with display ratio. A 4K (3840×2160) display is 16:9 because the pixel grid is itself 16:9; doubling resolution does not change the ratio.
Quick decision rules
- Buying a TV: stick with 16:9 unless you mostly watch cinematic film and have a dedicated home theater.
- Picking a monitor for productivity: 16:10 or 3:2 gives more vertical pixels than 16:9 at the same diagonal.
- Editing photos: keep an eye on the ratio of the final destination (Instagram 4:5, print 8×10, web banner 1.91:1) before composing.
- Designing for phone-first audiences: design at 9:16 first, then adapt for landscape, not the reverse.
Aspect Ratio FAQ
What is 16:9?
16:9 is an aspect ratio of 1.78 — the screen is 1.78 times as wide as it is tall. It is the standard for televisions, 1080p and 4K video, YouTube, and most laptops. A 1920 × 1080 image is 16:9, and so is 3840 × 2160.
What is the most common aspect ratio?
16:9. It covers essentially all televisions, the majority of laptops and desktop monitors, and both 1080p and 4K video. 9:16, its vertical sibling, is the standard for phone-first video.
What aspect ratio is 4K?
16:9. 4K UHD is 3840 × 2160, which reduces to 16:9. Increasing resolution adds pixels but does not change the shape of the frame. Cinema 4K (DCI 4K, 4096 × 2160) is the exception at 17:9.
Is 16:10 better than 16:9?
For documents, code and spreadsheets, yes — at the same diagonal a 16:10 panel is about an inch taller and an inch narrower, and the extra vertical pixels mean less scrolling. For film and games, 16:9 matches the source material and avoids letterboxing.
What is 21:9 in decimal?
About 2.37 for a 2560 × 1080 panel and 2.39 for 3440 × 1440. Neither is exactly 21 divided by 9 (2.33) — 21:9 is a marketing name for ultrawide panels close to the 2.39:1 cinema standard.
How do I calculate an aspect ratio?
Divide both dimensions by their greatest common divisor. 1920 and 1080 share a divisor of 120, which gives 16:9. To find a missing side, divide or multiply by the decimal: a 16:9 image 1500 px wide is 1500 ÷ 1.78 = 843 px tall.
What aspect ratio is a 65 inch TV?
16:9, like almost every television sold today. At that ratio a 65-inch diagonal gives a screen 56.7 inches wide and 31.9 inches tall (143.9 × 80.9 cm).
What is the aspect ratio of A4 paper?
√2:1, or about 1.414:1 — 210 × 297 mm. It is the only ratio that keeps its proportions when folded in half, which is why an A4 sheet folds into two A5 sheets of identical shape. See the A4 size guide.