Aspect Ratio Calculator
Simplify any width and height into a clean aspect ratio (16:9, 4:3, 21:9) for video editing, screen design, banner sizing and image cropping decisions.
Last updated: May 2026
Enter width and height to simplify the aspect ratio.
How it works
Enter any width and height to reduce them to the simplest whole-number ratio using the greatest common divisor. Useful when checking if a custom canvas matches a standard ratio, scaling video for a platform, or cropping an image to fit a specific format. A 1920×1080 image simplifies to 16:9; a 1280×1024 simplifies to 5:4.
Common ratios by platform
| Ratio | Common use | Example resolution |
|---|---|---|
| 16:9 | HD/4K video, YouTube, most monitors | 1920×1080, 3840×2160 |
| 4:3 | Classic TV, older monitors, some cameras | 1024×768, 1600×1200 |
| 21:9 | Ultrawide monitors, cinematic video | 2560×1080, 3440×1440 |
| 1:1 | Instagram posts, profile pictures | 1080×1080 |
| 9:16 | TikTok, Instagram Stories, Reels | 1080×1920 |
Frequently Asked Questions
What is an aspect ratio?
An aspect ratio is the proportional relationship between width and height, expressed as two numbers separated by a colon. For example, 1920–1080 simplifies to 16:9.
What are the most common aspect ratios?
16:9 is standard for HD video and most monitors. 4:3 is used in older displays and some cameras. 1:1 is used for square formats on social media.
Why do different platforms use different aspect ratios?
Aspect ratios evolved from the screens that use them. 16:9 became standard because it matches widescreen TVs and is efficient for cinema. 4:3 was the original television shape for decades. Social media platforms like Instagram started enforcing 1:1 (square) because mobile screens are portrait-oriented and square crops fit better in feeds. YouTube thumbnails are often 16:9. Knowing your platform's preferred ratio prevents awkward cropping or stretching.
What's the difference between landscape and portrait aspect ratios?
Landscape (wider than tall, like 16:9) is standard for monitors, TVs, and widescreen video. Portrait (taller than wide, like 9:16) is standard for mobile phones and social media stories. The same resolution (say, 1920 pixels) represents very different proportions in landscape vs portrait. Instagram Stories use 9:16 portrait; most YouTube videos use 16:9 landscape. Choosing the right orientation prevents forced black bars or letterboxing.
Do I need to know aspect ratio when I buy a monitor or TV?
Yes, if you care about how content displays. Most modern monitors and TVs are 16:9 widescreen. Some specialty monitors (like for professional video editing) might be 21:9 ultrawide, which stretches standard 16:9 video. Gaming monitors are often 16:9 or 16:10. If you watch a lot of old TV shows or classic films (4:3 aspect ratio), they'll display with black bars on a 16:9 screen, which is normal and unavoidable.