Dev & Web
Aspect Ratio Calculator
Calculate the aspect ratio from any width and height, or find the missing dimension from a known ratio. Quick presets for 16:9, 4:3, 1:1, 21:9, and more.
How it works
Enter any width and height to instantly see the simplified aspect ratio and its decimal equivalent. Switch to Ratio mode to calculate a missing dimension from a known ratio and one measurement.
Frequently asked questions
What is aspect ratio?
Aspect ratio is the proportional relationship between an image's width and height. A 16:9 ratio means for every 16 units of width, there are 9 units of height.
Why does aspect ratio matter for video?
Most modern video platforms (YouTube, TV, monitors) use 16:9. Using a different aspect ratio can result in black bars (letterboxing or pillarboxing) or cropped content.
How do I calculate aspect ratio from pixels?
Divide both dimensions by their greatest common divisor (GCD). For example, 1920÷120 = 16 and 1080÷120 = 9, giving 16:9.
What aspect ratio is best for social media?
Instagram feed: 1:1 (square) or 4:5 (portrait). Stories and Reels: 9:16. YouTube thumbnails: 16:9. Twitter/X headers: ~3:1.