What Is an Aspect Ratio?
An aspect ratio is the proportional relationship between the width and height of an image, video, or screen. It is always written as width:height — for example, 16:9 means the width is 16 units for every 9 units of height.
Understanding aspect ratios matters because displaying content at the wrong ratio causes:
- Stretching — objects look unnaturally wide or tall.
- Cropping — important parts of the image get cut off.
- Letterboxing or pillarboxing — black bars fill the empty space.
Use our free Aspect Ratio Calculator to instantly find the correct ratio and calculate matching dimensions for any width or height.
How to Calculate an Aspect Ratio
Finding the simplified ratio from pixel dimensions requires finding the Greatest Common Divisor (GCD):
- Take your width and height (e.g., 1920 × 1080).
- Find the GCD of both numbers (GCD of 1920 and 1080 is 120).
- Divide both by the GCD: 1920 ÷ 120 = 16, 1080 ÷ 120 = 9.
- Result: 16:9.
Our calculator does this instantly — just enter any width and height and you get the simplified ratio plus the ability to calculate a new matching dimension.
The Most Common Aspect Ratios and Where They Are Used
| Ratio | Resolution Examples | Used For |
|---|---|---|
| 16:9 | 1920×1080, 3840×2160, 1280×720 | YouTube, most TVs, laptop monitors, presentations |
| 9:16 | 1080×1920 | TikTok, Instagram Reels, YouTube Shorts, vertical videos |
| 4:3 | 1024×768, 1600×1200 | Classic TV, older monitors, some projectors |
| 1:1 | 1080×1080 | Instagram square posts, profile pictures |
| 4:5 | 1080×1350 | Instagram portrait feed (maximum vertical coverage) |
| 1.91:1 | 1200×628, 1080×566 | Instagram landscape, Facebook link previews |
| 21:9 | 3440×1440, 2560×1080 | Ultrawide monitors, cinematic films (2.35:1 to 2.39:1) |
| 3:2 | 6000×4000, 3000×2000 | DSLR cameras, 35mm film |
| 16:10 | 1920×1200, 2560×1600 | Older laptops, productivity monitors |
Platform-Specific Aspect Ratio Guide
YouTube
- Standard video: 16:9 — upload at 1920×1080 (Full HD) or 3840×2160 (4K).
- YouTube Shorts: 9:16 — 1080×1920.
- Videos with other ratios get letterboxed or pillarboxed to fit the 16:9 player.
- Square posts: 1:1 (1080×1080).
- Portrait posts: 4:5 (1080×1350) — maximizes screen space in the feed.
- Landscape posts: 1.91:1 (1080×566).
- Stories and Reels: 9:16 (1080×1920).
TikTok
- All content: 9:16 (1080×1920). TikTok is vertical-only.
- Feed posts: 1:1 or 4:5 for images, 16:9 for video.
- Link previews: 1.91:1 (1200×628 is the classic OG image size).
- Stories: 9:16.
Film and Cinema
- Standard widescreen: 16:9 (1.78:1).
- Cinematic widescreen: 2.35:1 or 2.39:1 (often labeled 21:9).
- IMAX: 1.43:1 or 1.9:1 depending on the theater.
How to Resize Without Distortion
If you know your desired new width, calculate the matching height using the ratio:
New Height = (Original Height ÷ Original Width) × New Width
Or if you know the desired height, calculate the width:
New Width = (Original Width ÷ Original Height) × New Height
Example: A 1920×1080 (16:9) image resized to 800 px wide:
- New Height = (1080 ÷ 1920) × 800 = 450 px
Our Aspect Ratio Calculator does this math instantly — enter your original dimensions and either the new width or new height, and it calculates the matching dimension.
Letterboxing and Pillarboxing
- Letterboxing: Black bars at the top and bottom. Happens when content is wider than the screen (e.g., a 21:9 movie on a 16:9 TV).
- Pillarboxing: Black bars on the left and right. Happens when content is narrower than the screen (e.g., 4:3 video on a 16:9 display).
- Windowboxing: Black bars on all four sides — the worst case, when content is both a different ratio and smaller than the screen.
Modern TVs and video players often have zoom or stretch options, but these either crop or distort the image. The best approach is to produce content in the native ratio of your target platform.
Aspect Ratios on Mobile Phones
Modern smartphones use very tall aspect ratios:
- iPhone 14/15: ~19.5:9 (2532×1170, 2556×1179 for Pro models)
- Samsung Galaxy S23/S24: ~19.5:9 or 20:9 (2340×1080)
- Google Pixel 8: 20:9 (2400×1080)
These ultra-tall ratios mean 16:9 content will have pillarboxing. Design mobile wallpapers at your phone’s native resolution for a perfect fit.
Aspect Ratio Calculator — Free, instant, private. Calculate any ratio, find matching dimensions, and explore common presets for every platform.