An aspect ratio is just the proportional relationship between width and height, written as two numbers — 16:9 means "for every 16 units of width, there are 9 units of height," regardless of the actual size. Here's where the common ones come from and when you'll actually run into them.
16:9 — The Video Standard
16:9 became the default for HD video and nearly every modern TV, monitor, and phone screen in landscape. 1920×1080, 1280×720, and 3840×2160 (4K) are all 16:9 — same shape, different resolution.
4:3 — The Old TV Standard
Before widescreen became standard, 4:3 (also written 1.33:1) was the shape of nearly every television and early computer monitor. You'll still see it in older video archives, some presentation software defaults, and certain camera sensors.
1:1 — Square
A perfect square, popularized by Instagram's original square-only post format. Still common for profile pictures, album covers, and social media grids where a uniform, predictable shape matters more than matching a screen.
9:16 — Vertical Video
The 16:9 ratio rotated 90° — the shape of a phone held upright, and the standard for Instagram/TikTok/YouTube Shorts-style full-screen mobile video.
21:9 — Ultrawide / Cinematic
Used by ultrawide monitors and closer to the wide aspect ratios used in cinema releases, 21:9 gives a noticeably wider field of view than standard 16:9, at the cost of not matching most standard video content without letterboxing.
“21:9” is really a marketing label. Common ultrawide resolutions don’t reduce to exactly 21:9: 2560×1080 simplifies to 64:27 (about 2.37:1) and 3440×1440 to 43:18 (about 2.39:1). Exact 21:9 would be 2.33:1. Cinema films are commonly released in 1.85:1 or about 2.39:1, which is why ultrawide screens show many films with little or no black bars.
3:2 — Classic Photography
The traditional 35mm film frame shape, still used by many digital cameras today. Slightly less wide than 16:9, more rectangular than 4:3. A 24-megapixel camera with a 3:2 sensor typically produces 6000Ă—4000 images.
4:5 and 16:10 — Two Ratios Worth Knowing
4:5 is a slightly tall portrait shape (for example 1080×1350) used for portrait posts in social feeds. It takes up more vertical space on a phone than a square without requiring full-screen vertical video. 16:10 (1.6:1) is a common laptop and monitor shape — 1920×1200 and 2560×1600 are both 16:10. It’s a little taller than 16:9, which gives more room for documents and code, but it means 16:9 video plays with thin bars above and below.
Quick Reference Table
| Ratio | Decimal (W Ă· H) | Example resolutions | Typical use |
|---|---|---|---|
| 16:9 | 1.78 | 1280Ă—720, 1920Ă—1080, 3840Ă—2160 | Video, TVs, most monitors |
| 16:10 | 1.60 | 1920Ă—1200, 2560Ă—1600 | Laptops, productivity monitors |
| 3:2 | 1.50 | 1080Ă—720, 6000Ă—4000 | Photography, some laptops and tablets |
| 4:3 | 1.33 | 1024Ă—768, 1600Ă—1200 | Older TV and video, presentations, tablets |
| 1:1 | 1.00 | 1080Ă—1080 | Profile pictures, album art, square posts |
| 4:5 | 0.80 | 1080Ă—1350 | Portrait social media posts |
| 9:16 | 0.56 | 1080Ă—1920 | Stories, Reels, Shorts, phone video |
| “21:9” | 2.33–2.39 | 2560×1080, 3440×1440 | Ultrawide monitors, cinematic video |
How to Calculate an Aspect Ratio
To simplify any width and height to a ratio, divide both by their greatest common divisor (GCD) — the largest number that divides both exactly.
- 1920Ă—1080: the GCD is 120. 1920 Ă· 120 = 16 and 1080 Ă· 120 = 9, so the ratio is 16:9.
- 1024Ă—768: the GCD is 256, giving 4:3.
- 1366×768: the GCD is only 2, giving 683:384. That’s about 1.779:1, so in practice it’s described as 16:9 (1.778:1) even though it isn’t exact.
That last example is why it helps to compare decimals as well as ratios: two sizes with nearly the same decimal look the same shape on screen.
How to Find a Missing Width or Height
If you know the ratio and one dimension, cross-multiply:
- Height = width Ă— (ratio height Ă· ratio width). A 1280px-wide 16:9 video: 1280 Ă— 9 Ă· 16 = 720px tall.
- Width = height Ă— (ratio width Ă· ratio height). A 1080px-tall 4:5 image: 1080 Ă— 4 Ă· 5 = 864px wide.
If the result isn’t a whole number, round it — and for video, round to an even number, since many video encoders require even dimensions.
Letterboxing, Pillarboxing and Cropping
When content and screen don’t share a ratio, something has to give. Letterboxing adds bars above and below (wide content on a narrower screen). Pillarboxing adds bars at the sides (4:3 or 9:16 content on a 16:9 screen). The alternative is cropping, which fills the screen but cuts off part of the picture. Stretching to fill is the one option to avoid: it distorts faces, text and circles.
If you record your screen with our browser screen recorder, the video takes the shape of whatever you shared — usually 16:9 or 16:10 for a full screen — so plan to crop if you’re posting it as vertical 9:16 video.
Aspect Ratios in CSS
The CSS aspect-ratio property keeps an element’s shape as its width changes, which is ideal for video embeds, thumbnails and cards:
.video-embed {
width: 100%;
aspect-ratio: 16 / 9;
}
.avatar {
width: 4rem;
aspect-ratio: 1; /* square */
object-fit: cover; /* crop the image instead of stretching it */
}Reserving space this way also stops the layout jumping while media loads. For more on keeping layouts in proportion across screen sizes, see What is Responsive Web Design?
Common Mistakes
- Confusing ratio with resolution. 1280Ă—720 and 3840Ă—2160 are both 16:9; the ratio says nothing about sharpness.
- Resizing only one dimension. Changing the width without recalculating the height distorts the image.
- Assuming phones are 16:9. Many modern phones are taller, around 19.5:9 or 20:9, so full-screen 9:16 video often shows small bars or is slightly cropped.
- Mixing up print size and pixel size. A ratio is the same in pixels or inches, but print size also depends on resolution — see what DPI and PPI mean.
Finding or Matching a Ratio
Given any width and height, you can find its simplified ratio, or work backward from a known ratio to a missing width or height — useful when resizing an image or setting up a video export without distorting it. Our Aspect Ratio Calculator does both instantly.
Frequently Asked Questions
Is 1080p always 16:9?
“1080p” refers to 1080 lines of vertical resolution. In everyday use it means 1920×1080, which is 16:9, but a 1080-pixel-tall video can have other widths — 1440×1080 is 4:3, for example.
Which ratio should I export video in?
Match where it will be watched: 16:9 for YouTube, websites and presentations, 9:16 for full-screen phone video, and 1:1 or 4:5 for feed posts. If you need several, shoot or record wider than you need and crop each version.
Why are aspect ratios sometimes written like 1.85:1?
That’s the same ratio expressed with a height of 1. Film uses this style because cinema ratios such as 1.85:1 and 2.39:1 don’t reduce to neat whole-number pairs.
Try it yourself: enter the width and height of an image or video you’re working on into the Aspect Ratio Calculator to see its simplified ratio, then enter that ratio and a known width to get the exact height you need (or a known height to get the width).