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.
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 |
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.