Aspect Ratio Calculator
Math & NumbersCalculate image and video aspect ratios. Resize dimensions while maintaining ratio for common 16:9, 4:3, 1:1 and custom formats.. Free, private — all processing in your browser.
The Aspect Ratio Calculator helps you work with image and video dimensions while maintaining their aspect ratio. Common ratios include 16:9 (HDTV, YouTube, most modern video), 4:3 (old TV, some monitors), 1:1 (Instagram square), 9:16 (TikTok/Stories vertical), 21:9 (ultra-wide cinematic), 3:2 (35mm film, DSLR), and custom.
Enter width or height plus desired ratio; the tool calculates the other dimension. Or enter both dimensions to see the current ratio and common equivalents. Great for creating thumbnails, resizing videos, designing banners, or working with screen dimensions.
Aspect Ratio Calculator — key features
Common ratio presets
16:9, 4:3, 1:1, 9:16, 21:9 and more.
Custom ratios
Any ratio you need.
Resize calculator
Enter one dimension, get the other.
Simplify dimensions
Shows simplified ratio (1920x1080 → 16:9).
Social media presets
YouTube, Instagram, TikTok, Twitter sizes.
Letterbox/crop visualizer
Shows how content fits different aspect ratios.
Batch calculation
Multiple aspect calculations at once.
Client-side only
All math in your browser.
How to use the Aspect Ratio Calculator
- 1
Enter ratio
Pick preset (16:9, 4:3, etc.) or enter custom like 21:9.
- 2
Enter one dimension
Width or height; tool calculates the other.
- 3
See result
Full dimensions displayed.
- 4
Optional — reverse
Enter both dimensions to find actual ratio.
- 5
Copy
One-click copy dimensions or ratio.
Common use cases for the Aspect Ratio Calculator
Video production
- →YouTube videos: 16:9 aspect for all standard video uploads.
- →Social vertical: 9:16 for TikTok, Stories, Reels.
- →Cinematic: 21:9 for letterboxed cinema aesthetic.
Design
- →Social banners: Cover image dimensions for each platform.
- →Print layout: Magazine and poster standard ratios.
- →Web banners: Hero images and ad banners.
Photography
- →Photo prints: Standard print sizes and their aspect ratios.
- →Social post crops: Square (1:1) vs portrait (4:5) for Instagram.
- →DSLR aspects: 3:2 standard DSLR, 4:3 smartphone.
Aspect Ratio Calculator — examples
YouTube thumbnail
16:9 ratio, 1280 width.
ratio 16:9, width 1280
height = 720. Final: 1280x720 pixels
Instagram square
1:1 ratio.
1:1, width 1080
height 1080. Square, 1080x1080
TikTok vertical
9:16 vertical.
9:16, width 1080
height 1920. Vertical 1080x1920
Simplify ratio
Find actual ratio.
1920x1080
ratio: 16:9 (simplified from 1920:1080)
Cinematic
21:9 ultra-wide.
21:9, height 1080
width 2520. Ultra-wide 2520x1080
Technical details
Aspect ratio is the proportional relationship between width and height. Typically expressed as W:H where the numbers indicate relative proportions.
Common aspect ratios and their decimal:
- 1:1 square = 1.0 (Instagram posts, old photos)
- 4:3 = 1.33 (old TVs, iPad, old monitors)
- 3:2 = 1.5 (35mm film, DSLR photos)
- 16:10 = 1.6 (some monitors)
- 16:9 = 1.78 (HDTV, modern monitors, YouTube, most video)
- 2:1 = 2.0 (some ultrawide content)
- 21:9 = 2.33 (cinematic, ultrawide monitors)
- 9:16 = 0.56 (vertical video for TikTok, Stories)
- 2.35:1 (1.85:1) = 2.35 (theatrical film)
Calculation:
- If ratio = W:H = R_w:R_h
- Given width: height = width × R_h / R_w
- Given height: width = height × R_w / R_h
Common presets for content creation:
- YouTube thumbnail: 1280×720 (16:9)
- Instagram post: 1080×1080 (1:1) or 1080×1350 (4:5)
- Instagram Story/Reels: 1080×1920 (9:16)
- Facebook cover: 820×312 (~2.6:1)
- Twitter post: 1200×675 (16:9)
- Pinterest pin: 1000×1500 (2:3)
- Email banner: 600×200 (3:1)
- Podcast cover: 3000×3000 (1:1)
Film aspect ratios:
- Academy ratio (old cinema): 1.375:1
- Widescreen (modern cinema): 1.85:1 or 2.35:1 (Cinemascope)
- IMAX: 1.44:1
Pixel aspect: most digital images have square pixels (1:1 pixel ratio). Some video formats have non-square pixels requiring adjustment.
GCD simplification: 1920:1080 simplifies to 16:9 (divide both by 120). Shows simplified form for clarity.
Conversions between aspect ratios:
- Letterbox: fitting wider content (16:9) in narrower container (4:3) with black bars top/bottom
- Pillarbox: fitting narrower (4:3) in wider (16:9) with black bars left/right
- Crop: remove edges to fit new aspect
- Stretch: distort proportions (usually avoid)
Common problems and solutions
⚠Ratio rounded wrong
1920:1080 is exactly 16:9. But 1600x900 is also 16:9. Simplify to find canonical form. GCD of 1920 and 1080 is 120; divide both by 120 to get 16:9.
⚠Non-standard output
Forcing custom ratios creates unusual dimensions. Check your target platform supports non-standard aspect ratios before committing.
⚠Pixel rounding
Aspect ratio calculations may produce fractional pixels. Always round to integers; slight aspect deviation (0.1%) imperceptible.
⚠Letterbox vs crop
Fitting wider content in narrower aspect: letterbox adds black bars. Alternative: crop edges. Choose based on content importance at edges.
⚠Non-square pixels
Some video formats have non-square pixels. 720x480 NTSC is 4:3 with non-square pixels; pixel aspect ratio adjustment needed. Modern video usually square pixels.
⚠Platform variations
Instagram supports 1:1 and 4:5; Twitter has different in-stream ratios. Check current specs, which change.
⚠Aspect confusion
16:9 is wider than tall; 9:16 is taller than wide (vertical video). Same ratio, different orientation.
Aspect Ratio Calculator — comparisons and alternatives
Compared to manual calculation, this tool handles GCD simplification and cross-dimension math automatically.
Compared to guessing pixel dimensions, this tool ensures you hit exact aspect ratios for platforms.
Compared to image editor \\\"constrain proportions\\\" checkbox, this tool calculates target dimensions before you open the editor.
Frequently asked questions about the Aspect Ratio Calculator
▶What is aspect ratio?
Proportional relationship between width and height. Written as W:H. 16:9 means 16 units wide for every 9 units tall.
▶What is 16:9?
Standard HDTV and modern video aspect ratio. For every 16 units of width, the content is 9 units tall. 1920x1080, 1280x720, 3840x2160 are all 16:9.
▶How do I resize while maintaining ratio?
If ratio = W:H, new_height = new_width × H/W. For 16:9, height = width × 9/16. 1280 width → 720 height.
▶Why is 1920x1080 called 16:9?
Simplify fraction: divide both by GCD of 1920 and 1080, which is 120. 1920/120 = 16; 1080/120 = 9. So 1920:1080 reduces to 16:9.
▶What’s best aspect for Instagram?
Multiple accepted. 1:1 (1080x1080) classic square. 4:5 (1080x1350) tall — vertical. 9:16 (1080x1920) Stories/Reels. Posts can be landscape 1.91:1 (similar to Twitter). Check platform current specs.
▶Is my data private?
Yes. All calculation in your browser.
▶What is a letterbox?
Black bars top/bottom when fitting wider content (16:9) in narrower container (4:3). Content keeps full aspect; bars fill unused space.
▶What’s the golden ratio?
1.618:1 proportion, found in nature and classical design. Occasionally used for aesthetically pleasing aspect ratios. Not standard in tech but sometimes referenced.
Additional resources
- Aspect ratio Wikipedia — Background on image aspect ratios.
- Display aspect ratio — Standard display aspect ratios.
- Social media image sizes — Up-to-date platform dimensions.
- Film aspect ratios — Cinema aspect ratios and history.
- YouTube upload specs — YouTube’s video specifications.
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