Aspect Ratio Calculator
Scale images and videos without distortion, simplify any ratio to its lowest terms, and see the shape update live as you type.
Enter the original dimensions and a new width to find the height.
Step-by-step solution
Choose a mode and enter values to see the working
Aspect Ratio Calculator Explained
Core concepts, classroom applications, and plain-English explanations for all audiences.
When would you actually use this?
TV screens are 16:9 — 16 units wide for every 9 units tall. TikTok and Instagram Reels use 9:16 (portrait flipped). Cinema widescreen is 2.39:1. Whenever you crop a photo, resize a video, or set up a projection screen, you're working with aspect ratios to avoid stretching or black bars.
Worked example
"A 16:9 video needs to fit in a 1200 px wide space. What height does it need to be?"
Ratio: 16:9 → width/height = 16/9
1200 / height = 16 / 9
height = 1200 × 9 / 16 = 675 px
Shortcut: multiply width by 0.5625 (= 9/16) for any 16:9 calculation.
Common aspect ratios
- → 16:9 — HD and 4K television, YouTube, desktop monitors.
- → 4:3 — older TV, standard photography, tablet screens.
- → 1:1 — square format, Instagram posts.
- → 2.39:1 — cinema widescreen (anamorphic).
Simplifying a ratio
1920:1080 simplifies to 16:9 — divide both by the HCF (120). Always simplify before comparing aspect ratios.
What is Aspect Ratio?
Aspect ratio describes the proportional relationship between an image's width and its height. It's usually expressed as two numbers separated by a colon, like 16:9 or 4:3. The first number represents the width, and the second represents the height.
Understanding aspect ratio is crucial for anyone working with visuals – from web developers ensuring images fit perfectly, to designers creating layouts, photographers framing shots, and students learning about digital media. It ensures your content looks correct and isn't stretched, squashed, or cropped unintentionally.
Our Aspect Ratio Calculator helps you easily find missing dimensions, simplify complex ratios, and visualise the shape of your content.
Common mistakes to avoid
- Cropping an image to fit a new aspect ratio without considering the content:Cropping removes parts of your image, potentially losing important visual information, context, or artistic intent. Scale the image proportionally to fit the new aspect ratio, or carefully reframe the shot if cropping is absolutely essential and doesn't compromise the message.
- Assuming a ratio like 9:16 means 9 units wide by 16 units high for a landscape image:Aspect ratios are almost universally expressed as Width:Height. Mixing them up leads to incorrect dimensions and distorted visuals (e.g., a stretched landscape image). Always remember the standard W:H format. For portrait content, the ratio might be 9:16 (meaning 9 wide, 16 high), but it's still W:H.
- Using large numbers like 3840:2160 directly in calculations or descriptions:While technically correct, large numbers make ratios harder to understand, compare, and work with. It's not the simplest form. Always simplify ratios to their smallest whole numbers (e.g., 16:9 for 3840:2160) using the Greatest Common Divisor (GCD). Our calculator's 'Simplify' mode does this for you.
- Incorrectly calculating a missing dimension, for example, for a 16:9 ratio with a width of 1280px, calculating (1280 / 9) * 16 to find the height:This calculation would invert the ratio. You're effectively trying to find the width based on a height of 1280px, not the height based on a width of 1280px. The correct formula is (known_dimension / known_ratio_part) unknown_ratio_part. So, for 16:9 and width 1280: (1280 / 16) 9 = 80 * 9 = 720.