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 |
Verifying ratio before exporting for platforms
Platform specifications for image and video content change without announcement, and the ratio of an export file is not always obvious from the resolution alone. A canvas of 1200 by 628 pixels is not 16:9 (which would be 1200 by 675) but approximately 1.91:1, which is the ratio Facebook and LinkedIn prefer for link preview images. A 1280 by 720 export is correctly 16:9, but a 1280 by 800 canvas (common in some design tools as a default) is 16:10 and will be cropped or pillarboxed on any 16:9 display. Simplifying the dimensions to their base ratio before exporting catches these mismatches before they reach the platform.
Video editors encounter this most often when working with footage from cameras that shoot at non-standard sensor sizes. A camera recording 3840 by 2160 is true 4K at 16:9. A micro-four-thirds sensor shooting 4096 by 3072 is roughly 4:3, and dropping that footage into a 16:9 timeline without reframing produces pillarboxing. Checking the ratio at the start of a project rather than at export avoids rework when the timeline crop settings are already set. For animated banner advertising, ad networks specify exact ratios in their creative guidelines, and a ratio mismatch causes the ad to be rejected at upload regardless of file size or format compliance.
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.