Calculate image aspect ratio, find missing dimensions, resize while maintaining ratio, and get ratios for common screen sizes.
Aspect Ratio Calculator
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Common Ratios
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Aspect Ratio: What It Is and Why It Matters
Aspect ratio is the proportional relationship between an image's width and height, expressed as W:H. A 1920×1080 image has a 16:9 ratio. Understanding aspect ratios is essential for responsive design, video production, print layout, and ensuring images display correctly across devices.
Common Aspect Ratios and Their Uses
16:9 — Standard HD/4K video, YouTube, monitors, most TVs
4:3 — Old TVs, standard monitors pre-2003, some iPads
1.91:1 (≈1200:630) — Open Graph meta images for social sharing
3:2 — Full-frame DSLR camera default, 35mm film
Maintaining Aspect Ratio When Resizing
If you know the original dimensions (1920×1080) and want to resize to a width of 800, the new height = 800 × (1080/1920) = 450. This keeps the 16:9 ratio. This calculator automates that math — enter the new width and it calculates the correct height.
Frequently Asked Questions
YouTube recommends 16:9 aspect ratio for standard videos. Common resolutions: 1920×1080 (1080p), 2560×1440 (1440p), 3840×2160 (4K). YouTube Shorts use 9:16 vertical ratio (1080×1920). If you upload a video with a different aspect ratio, YouTube adds black bars (letterboxing/pillarboxing) to fill the 16:9 player.
Modern iPhones (iPhone X and later) have a 19.5:9 ratio (approximately 2:1 or tall). The actual pixel resolution varies by model: iPhone 15 is 2556×1179 pixels. For full-screen iPhone video/stories, use 9:16 (1080×1920) which crops slightly on iPhones but is the universal vertical video standard.
Divide both dimensions by their Greatest Common Divisor (GCD). For 1920×1080: GCD(1920,1080) = 120. 1920÷120=16, 1080÷120=9. Result: 16:9. If the GCD is 1 (or a prime), you can simplify the ratio manually to the nearest common ratio (e.g. 1200×630 → GCD=30 → 40:21, but commonly called 1.91:1).
Social media platforms crop images to their required ratio. Facebook crops to 1.91:1 for link previews (1200×630). Instagram crops to 1:1 for grid feed posts. Twitter crops to roughly 2:1. If your image doesn't match, the platform auto-crops, often cutting out important content. Always design to the platform's target aspect ratio to control what's visible.