OTHER · ASPECT RATIO
Aspect Ratio Calculator
Calculate the aspect ratio of any image, video, or screen, and scale dimensions proportionally. Simplifies ratios like 1920×1080 to 16:9 and computes missing width or height.
About This Calculator
Enter the original width and height of any image, video frame, or screen to calculate its simplified aspect ratio (e.g., 1920×1080 = 16:9). Then use scale mode to find the missing dimension — enter a new width to get the proportional height, or enter a new height to get the proportional width. Preset buttons for common display ratios let you jump straight to 16:9, 4:3, 21:9, and more.
How It Works
The simplified ratio W:H is calculated by dividing both dimensions by their greatest common divisor (GCD). The decimal ratio = width ÷ height. To scale: scaledHeight = newWidth × (height ÷ width); scaledWidth = newHeight × (width ÷ height). Results are rounded to the nearest pixel. The closest common ratio is matched within 1% tolerance against 9 standard display ratios.
The Formula
ratio = W/GCD : H/GCD
- W
- original width (px)
- H
- original height (px)
- GCD
- greatest common divisor of W and H
Frequently Asked Questions
- What does 16:9 mean?
- 16:9 means the width is 16 units for every 9 units of height. This is the standard widescreen aspect ratio used by HD (1280×720), Full HD (1920×1080), 4K (3840×2160), and most modern monitors and televisions. When you see a 16:9 ratio in a video player, the frame fills the entire screen without black bars on typical widescreen displays.
- How do I keep an image proportional when resizing?
- Use 'scale height' mode: enter the new width you want and the calculator returns the height that maintains the original ratio. Use 'scale width' mode to do the reverse. Never stretch an image by changing only one dimension without using this tool — it distorts the aspect ratio and makes the image look squashed or stretched.
- What is the difference between 4:3 and 16:9?
- 4:3 (1.33:1) is the traditional standard-definition TV and older computer monitor ratio — it's nearly square. 16:9 (1.78:1) is modern widescreen — significantly wider. When you play older 4:3 content on a 16:9 screen, you typically see black bars on the sides (pillarboxing). When 16:9 content plays on a 4:3 display, black bars appear top and bottom (letterboxing).
- Why does my ratio show as 8:5 instead of 16:10?
- 8:5 and 16:10 are mathematically identical — both simplify to the same decimal ratio (1.6:1). The calculator always simplifies to the smallest integer ratio using the greatest common divisor. Many 16:10 monitors are described that way for marketing clarity, but the simplified form is 8:5. Both representations are correct.