Image ResizerImage Tools
Resizes images to exact pixels or a percentage, one at a time or in batches.
Aspect Ratio Calculator
Find the aspect ratio of any width and height, or the missing side for a given ratio. The aspect ratio calculator has presets for 16:9, 4:3, 21:9, and other common formats.
Runs in your browser. Your data is not uploaded.
How to use the Aspect Ratio Calculator
- Choose Ratio from a size or Missing side from a ratio.
- Enter the width and height, or pick a ratio and enter the one side you know.
- Press Calculate. You get the ratio or the new size, with a preview rectangle.
How it works
ratio = (width ÷ gcd) : (height ÷ gcd) height = width × ratio height ÷ ratio width width = height × ratio width ÷ ratio height
gcd is the greatest common divisor of the width and height, found with Euclid's algorithm.
Examples
- 1920 × 1080: the gcd is 120, so the ratio is 16:9.
- 16:9 at a width of 1280: height = 1280 × 9 ÷ 16 = 720.
- 2560 × 1080 is exactly 64:27, which is sold as 21:9 ultrawide.
Common aspect ratios
- 16:9: HD, 4K, most monitors and YouTube
- 9:16: vertical video for Reels, TikTok, and Shorts
- 4:3: older TVs and iPads
- 3:2: many camera sensors and Surface laptops
- 16:10: many laptops, such as 1440 × 900
- 1:1: square posts
After finding the dimensions for a web image, use the image resizing and compression guide to reduce its download size.
Limitations
- Decimal sizes are shown as a ratio to 1, such as 1.7778:1.
- Resized sides may not be whole pixels; the rounded size is shown too.
Frequently asked questions
What aspect ratio is 1920 × 1080?
16:9.
How do I calculate aspect ratio?
Divide the width and height by their greatest common divisor.
What is the height of 16:9 at 1280 wide?
720 pixels.
Related tools
Often used together with Aspect Ratio Calculator.
Image CropperImage Tools
Crops images with a draggable box, aspect ratio presets, and exact pixel fields.
Screen Resolution CheckerInternet Tools
Your screen size, viewport, pixel ratio, and display settings.