Find the ratio of any dimensions, scale images proportionally, and explore common ratios for video, photo and design.
An aspect ratio is the proportional relationship between width and height. A 1920×1080 image has a GCD of 120 — dividing both by 120 gives 16:9. The ratio defines the shape, not the actual size. Two images at 640×360 and 3840×2160 have the same 16:9 ratio.
16:9 is the dominant ratio for HD and 4K video, YouTube, Netflix, most monitors, and smartphone landscape video. It replaced the 4:3 ratio of CRT televisions. The choice of 16:9 was a compromise between the 4:3 TV standard and 2.35:1 cinema format.
9:16 (the inverse of 16:9) is the standard for TikTok, Instagram Reels, YouTube Shorts, and Snapchat Stories. It fills the entire smartphone screen when held vertically, giving maximum visual impact on mobile platforms.
To resize without distortion, both dimensions must change by the same factor. If the new width is 1280 and original was 1920, the factor is 1280/1920 = 0.667. Multiply the original height (1080) by 0.667 to get 720. Use the Scale tab to do this automatically.
Print size depends on pixel count and DPI (dots per inch). A 3000×2000px image at 300 DPI prints at 10×6.67 inches. At 72 DPI (screen resolution) the same file would be 41.7×27.8 inches — useful for large-format banners, terrible for sharp photo prints.
Modern CSS makes aspect ratio maintenance easy: aspect-ratio: 16 / 9. Set width to 100% and height adjusts automatically. The CSS Code tab generates ready-to-use code for any ratio, including the older padding-top hack for legacy browser support.
| Name | Resolution | Ratio | Used For |
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An aspect ratio is the proportional relationship between width and height of a rectangular shape, expressed as two numbers separated by a colon (e.g., 16:9). It describes the shape of the image but not its actual size. Two images with the same aspect ratio look the same shape whether they are 100×56 pixels or 3840×2160 pixels. Aspect ratios are used in photography, film, television, display technology, and web design to ensure images display correctly without distortion or cropping.
16:9 — Modern TV, YouTube, HD/4K video, most PC monitors. 4:3 — Old TV, iPad, some tablets. 1:1 — Instagram square, album covers. 9:16 — TikTok, Reels, Shorts (vertical video). 3:2 — Most DSLR cameras (35mm film). 4:5 — Instagram portrait posts. 21:9 — Ultra-wide monitors and cinema screens. 2:1 — Some cinema cameras and drone footage.
Find the Greatest Common Divisor (GCD) of the width and height, then divide both values by the GCD. Example: 1920×1080 — the GCD is 120. 1920÷120=16 and 1080÷120=9, so the ratio is 16:9. This tool does the calculation automatically using the Euclidean algorithm. Simply type your width and height into the Find Ratio tab.
1920×1080 has a 16:9 aspect ratio — the standard Full HD (1080p) resolution. Other common 16:9 resolutions: 1280×720 (HD / 720p), 2560×1440 (QHD / 1440p), 3840×2160 (4K / 2160p), and 7680×4320 (8K). All these share the same shape ratio even though their pixel counts differ greatly.
Always scale proportionally by changing both dimensions by the same factor. Use the Scale tab: enter your original dimensions and either the new width or height — the other dimension is calculated automatically. In design software, hold Shift while dragging a corner handle to lock the aspect ratio. In CSS, set only width or height and let the other be auto.
YouTube recommends 16:9 thumbnails at 1280×720 pixels minimum. This matches the player aspect ratio and fills the slot without black bars. For YouTube Shorts, use 9:16 (1080×1920). Keep thumbnails under 2 MB in JPG, PNG, GIF, or BMP format.
Standard 4K (3840×2160) has a 16:9 ratio — same as 1080p, just four times more pixels. Cinema 4K (4096×2160) has a slightly wider ratio of approximately 1.9:1. Some 4K formats like DCI 4K (4096×1714) use the 2.39:1 anamorphic cinema ratio.
For a sharp 8×10 inch print at 300 DPI (the standard for photo printing), you need at least 2400×3000 pixels (8×300 = 2400, 10×300 = 3000). For 150 DPI draft quality, 1200×1500 pixels is sufficient. For a billboard viewed from a distance, even 72 DPI may look sharp. Use the Pixel → Print tab to calculate any resolution/DPI combination.
The CSS aspect-ratio property sets a preferred aspect ratio for an element: aspect-ratio: 16 / 9;. Set the width (e.g., width: 100%) and the height adjusts automatically. Supported in all modern browsers. For older browser support, use the padding-top hack: set padding-top: 56.25% (9/16 × 100%) on a relatively-positioned container. The CSS Code tab generates both approaches for any ratio you enter.
2.35:1 (also written as 2.35:1 or 235:100) is the anamorphic widescreen cinema ratio used by many Hollywood films. It creates the dramatic wide-screen "letterbox" look with black bars at the top and bottom when displayed on a 16:9 screen. Modern cinema often uses 2.39:1 (DCI standard). Films like Lawrence of Arabia, The Dark Knight, and Mad Max: Fury Road use this ultra-wide format.