Aspect Ratio Calculator
Find the exact aspect ratio of any width and height pair, or scale one dimension to match a target while keeping the original proportions perfectly intact.
Original Dimensions
Common presets
Common Aspect Ratios Reference
| Ratio | Common Use | Example Resolution |
|---|---|---|
| 16:9 | HD/4K TV, YouTube, monitors | 1920×1080 |
| 4:3 | Legacy monitors, film scan | 1024×768 |
| 1:1 | Instagram, avatar, square | 1080×1080 |
| 21:9 | Ultrawide cinema monitors | 2560×1080 |
| 9:16 | Mobile video, Stories, Reels | 1080×1920 |
| 3:2 | DSLR cameras, 35mm film | 6000×4000 |
| 2:1 | Cinematic wide format | 2048×1024 |
Quick answer
An aspect ratio expresses the proportional relationship between a rectangle's width and its height, written as W:H. To find it, divide both the width and height by their greatest common divisor (GCD). For example, a 1920×1080 image has a GCD of 120, giving the ratio 16:9. To scale dimensions proportionally, multiply or divide both values by the same factor so the ratio stays constant. Common ratios include 16:9 (widescreen HD), 4:3 (traditional TV/monitor), and 1:1 (square).
Formula & method
Ratio = (W / GCD(W, H)) : (H / GCD(W, H))
- W — Width in pixels (or any unit)
- H — Height in pixels (or any unit)
- GCD(W,H) — Greatest common divisor of width and height
Simplify width and height by dividing both by their greatest common divisor to get the canonical ratio.
New H = New W × (H / W)
- New W — The desired target width
- H / W — The original aspect ratio as a decimal multiplier
- New H — The resulting height that preserves the ratio
Scale height proportionally when a new target width is provided.
New W = New H × (W / H)
- New H — The desired target height
- W / H — The original aspect ratio as a decimal multiplier
- New W — The resulting width that preserves the ratio
Scale width proportionally when a new target height is provided.
Examples
- Input
- Width = 1920, Height = 1080
- Result
- 16:9
- Why
- GCD(1920, 1080) = 120. Dividing both values: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, yielding the standard 16:9 widescreen ratio.
- Input
- Original 1920×1080, target width = 1280
- Result
- 1280×720
- Why
- New height = 1280 × (1080 / 1920) = 1280 × 0.5625 = 720. The scaled resolution is 1280×720, still 16:9.
- Input
- Width = 2560, Height = 1440
- Result
- 16:9
- Why
- GCD(2560, 1440) = 160. Dividing: 2560 ÷ 160 = 16 and 1440 ÷ 160 = 9. QHD is also a 16:9 display, just at higher resolution.
- Input
- Width = 800, Height = 600
- Result
- 4:3
- Why
- GCD(800, 600) = 200. Dividing: 800 ÷ 200 = 4 and 600 ÷ 200 = 3. This is the classic 4:3 ratio used by traditional monitors and early TV.
Frequently asked questions
What is an aspect ratio?
An aspect ratio is the proportional relationship between the width and height of a rectangle, expressed as two integers separated by a colon (W:H). It describes shape without specifying exact size, so 1920×1080 and 1280×720 share the same 16:9 ratio.
What are the most common aspect ratios?
16:9 is the dominant standard for HD and 4K televisions, YouTube, and modern monitors. 4:3 was the standard for older CRT monitors and TVs. 1:1 is used for square formats like Instagram posts. 21:9 is used for ultrawide cinematic monitors, and 9:16 is the vertical format for mobile video and stories.
How do I scale dimensions without distortion?
Enter your original width and height, then enter only the target width or the target height. The calculator will compute the missing dimension using the original ratio (New H = New W × H/W, or New W = New H × W/H), guaranteeing no stretching or squishing.
Why does my video look stretched or squished?
Stretching occurs when the display or container uses a different aspect ratio than the source content. For example, displaying a 16:9 video in a 4:3 box without letterboxing will stretch the image horizontally. Always match or letterbox/pillarbox to preserve the original ratio.
What is the difference between aspect ratio and resolution?
Resolution specifies the exact number of pixels (e.g., 1920×1080), while aspect ratio only describes the shape (e.g., 16:9). Many different resolutions can share the same aspect ratio — 3840×2160 (4K), 1920×1080 (Full HD), and 1280×720 (HD) are all 16:9.
How is the greatest common divisor (GCD) used in aspect ratios?
The GCD of two numbers is the largest integer that divides both without a remainder. By dividing width and height each by their GCD, you reduce the pair to its smallest whole-number ratio. For instance, GCD(1920, 1080) = 120, so 1920/120 = 16 and 1080/120 = 9, giving 16:9.
Sources & references
- https://www.w3schools.com/css/css_rwd_mediaqueries.asp
- https://developer.mozilla.org/en-US/docs/Web/CSS/aspect-ratio
- https://en.wikipedia.org/wiki/Aspect_ratio_(image)
External references open in a new tab. We are independent and not affiliated with these organizations.
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- ✓ No sign-up required
- ✓ Runs entirely in your browser — nothing is uploaded.
- ✓ Formula and method shown above
Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.
Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.
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