Calculate, convert, and resize aspect ratios for video, images, and screens. Get the exact width or height you need without distortion.
Calculate Aspect Ratio
Enter width and height to find the simplified aspect ratio.
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16:9
📐 Aspect Ratio—
📏 Decimal Ratio—
🔢 GCD—
📷 Common Match—
Resize Keeping Aspect Ratio
Enter original dimensions and one new dimension — we calculate the other.
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×
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Width
×
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Height
📐 Aspect Ratio—
🔢 Scale Factor—
Common Aspect Ratios
Click any ratio to pre-fill the calculator.
Platform Size Reference
Recommended dimensions for major platforms.
Platform
Format
Ratio
Recommended Size
YouTube
Video
16:9
1920×1080 (1080p) or 3840×2160 (4K)
YouTube
Shorts
9:16
1080×1920
YouTube
Thumbnail
16:9
1280×720 (min)
Instagram
Feed Square
1:1
1080×1080
Instagram
Feed Portrait
4:5
1080×1350
Instagram
Stories / Reels
9:16
1080×1920
TikTok
Video
9:16
1080×1920
Twitter/X
Post Image
16:9
1200×675
Twitter/X
Header
3:1
1500×500
Facebook
Post
1.91:1
1200×628
LinkedIn
Post
1.91:1
1200×628
Zoom / Video Call
Background
16:9
1920×1080
Full HD Monitor
Screen
16:9
1920×1080
4K Monitor
Screen
16:9
3840×2160
iPad
Screen
4:3
2048×1536
Complete Guide to Aspect Ratios
An aspect ratio defines the proportional relationship between a frame's width and height. Whether you're editing video, designing social media graphics, or building a website, understanding aspect ratios ensures your content displays correctly on every screen without unwanted cropping or stretching. Our aspect ratio calculator lets you instantly find the ratio from any pixel dimensions, or resize to a new size while keeping the ratio locked.
How to Calculate Aspect Ratio
The aspect ratio of any rectangle is found by dividing both dimensions by their Greatest Common Divisor (GCD) — the largest number that divides both exactly. For example, 1920×1080: the GCD of 1920 and 1080 is 120. So 1920÷120=16 and 1080÷120=9, giving 16:9. For 2560×1080: GCD is 40, giving 64:27 — a common ultrawide monitor ratio. This calculator handles the math instantly for any dimensions you enter.
Resizing Images Without Distortion
To resize an image while maintaining its aspect ratio, use the proportion formula: new height = (new width × original height) ÷ original width. For example, resizing a 1920×1080 image to 800px wide: new height = (800 × 1080) ÷ 1920 = 450px. The resized image is 800×450 — still 16:9. Our resize calculator automates this for any combination of dimensions.
Letterboxing vs Pillarboxing vs Cropping
When content doesn't match the display ratio, there are three ways to handle it: Letterboxing adds black bars top and bottom (e.g. watching 21:9 film on 16:9 TV). Pillarboxing adds black bars on sides (e.g. watching 4:3 content on 16:9). Cropping cuts off edges to fill the frame. For professional results, always create content at the target platform's native ratio.
Frequently Asked Questions
An aspect ratio is the proportional relationship between the width and height of an image, video, or screen. It is written as width:height (e.g. 16:9). A 16:9 ratio means for every 16 units of width, there are 9 units of height. Aspect ratios are used in video production, photography, web design, and social media to ensure content displays correctly without stretching or cropping.
16:9 is the most common aspect ratio today, used by YouTube, most TVs, monitors, and smartphones in landscape mode. 4:3 was the standard before widescreen. 1:1 (square) is popular on Instagram. 9:16 (vertical) is used for TikTok, Instagram Reels, and YouTube Shorts. 21:9 is used for ultrawide monitors and cinematic content.
To calculate the aspect ratio, divide both the width and height by their Greatest Common Divisor (GCD). For example, 1920×1080: GCD is 120, so 1920÷120 = 16 and 1080÷120 = 9, giving 16:9. Our calculator does this automatically — just enter your width and height.
Enter your original width and height, then enter the new width or height you want. Our calculator will automatically calculate the other dimension to maintain the exact aspect ratio. This prevents distortion and stretching.
YouTube recommends 16:9 (1920×1080 for Full HD, 3840×2160 for 4K, 1280×720 for HD). YouTube Shorts use 9:16. If you upload a video with a different ratio, YouTube adds black bars (letterboxing or pillarboxing) to fit the 16:9 player.
Instagram supports multiple ratios: 1:1 (square, 1080×1080) for feed posts, 4:5 (portrait, 1080×1350) for maximum screen coverage in feed, 1.91:1 (landscape, 1080×566) for horizontal photos, and 9:16 (1080×1920) for Stories and Reels.
16:9 is the standard widescreen ratio used by most TVs, monitors, and video content. 16:10 is slightly taller, commonly used in older laptops and some professional monitors. It provides more vertical space for reading and productivity. At 1920px wide: 16:9 = 1080px tall, 16:10 = 1200px tall.
Letterboxing adds black horizontal bars (top and bottom) when content is wider than the screen — common when watching 21:9 movies on a 16:9 TV. Pillarboxing adds black vertical bars (left and right) when content is narrower — common when watching 4:3 content on a 16:9 screen.
Modern iPhones (iPhone X and later) use approximately 19.5:9 (2532×1170 for iPhone 14). Older iPhones used 16:9. The tall screen ratio means content designed for 16:9 will have letterboxing. For iPhone wallpapers and apps, design for the native resolution of the specific model.
Right-click the file and check Properties (Windows) or Get Info (Mac) to see width × height in pixels. Then use our calculator to convert those pixel dimensions into the simplified aspect ratio. For example, 2560×1440 → 16:9.