Need to size a video, image, or design without stretching it? This aspect calculator helps you quickly find the ratio of any dimensions and calculate a missing width or height while preserving proportions.
Aspect Ratio Calculator
Use either section below: find the ratio from dimensions, or compute a missing side from a known ratio.
1) Find ratio from width and height
2) Calculate missing dimension from ratio
What is an aspect ratio?
Aspect ratio is the proportional relationship between width and height. It is usually written as W:H, like 16:9 or 4:3. A ratio does not define absolute size; it defines shape. For example, 1600×900 and 1920×1080 are different sizes but the same aspect ratio: 16:9.
The basic formula
To get the raw ratio as a decimal, divide width by height:
- ratio decimal = width / height
- Then simplify width and height by dividing both by their greatest common divisor (GCD).
- Example: 1920×1080 → divide both by 120 → 16:9.
Why aspect ratio matters
Using the wrong aspect ratio causes stretched images, squashed video, awkward crops, and layout issues. If you work with YouTube videos, Instagram reels, presentations, web banners, or UI mockups, ratio consistency is one of the easiest ways to keep everything looking professional.
- Video editing: avoids black bars and distortion.
- Photography: controls framing for print and digital displays.
- Web design: keeps media responsive and aligned.
- Social media: helps you export to platform-friendly dimensions.
Common aspect ratios and where they are used
- 1:1 — profile pictures, square posts.
- 4:3 — older displays, slides, some cameras.
- 3:2 — DSLR and mirrorless camera photo formats.
- 16:9 — HD video, YouTube, TVs, modern presentations.
- 16:10 — many laptops and productivity monitors.
- 21:9 — cinematic and ultrawide formats.
- 9:16 — vertical stories, shorts, and reels.
How to use this calculator effectively
Find a ratio from existing dimensions
Enter width and height from your source media. The calculator returns:
- The simplified aspect ratio
- The decimal form (useful in development and CSS)
- Orientation (landscape, portrait, or square)
- A closest common standard ratio when applicable
Compute a missing side without distortion
If you already know the ratio (for example, 16:9) and one side, enter either width or height. The calculator will compute the matching dimension to preserve exact proportions.
Practical examples
- Want a 16:9 thumbnail at 1280px wide? Height should be 720px.
- Need a 9:16 mobile video with height 1920px? Width should be 1080px.
- Image is 3000×2000? That simplifies to 3:2.
Final tip
Aspect ratio is all about consistency. Decide your target ratio first, then resize all assets around it. This reduces editing time, prevents quality loss from repeated crops, and helps your content look clean across devices.