Aspect ratio calculator

1. 1

   Enter a size

   Type a width and height, or read them from an image or video file. The file stays on your computer.

2. 2

   Read the ratio

   See the ratio in whole numbers and as a decimal, and the common ratio it's closest to.

3. 3

   Resize to a ratio

   Pick your ratio or a common one, type a new width or height, and get the other side.

An aspect ratio is width to height, divided down by the largest number that goes into both. 1920 × 1080 divides by 120 into 16:9; 1080 × 1350 divides by 270 into 4:5.

Some sizes don't reduce to small numbers. 1366 × 768, a common laptop screen, reduces to 683:384, which is 1.78:1 and 0.05% off 16:9, so it's called 16:9 in practice.

The ratios below cover most of what you'll post. YouTube asks for 16:9 thumbnails, and Instagram keeps photo posts whole between 1.91:1 and 3:4.

• 9:16, 1080 × 1920: TikTok, Reels, Shorts and Stories.
• 16:9, 1920 × 1080 or 3840 × 2160: YouTube videos and thumbnails.
• 4:5, 1080 × 1350, and 3:4, 1080 × 1440: Instagram portrait posts.
• 1:1, 1080 × 1080: square posts.
• 1.91:1, 1080 × 566: Instagram landscape posts.

Changing one side by the ratio keeps the picture's shape. Moving to a different ratio, such as 16:9 footage into a 9:16 video, needs a crop or bars; stretching to fit distorts faces and text.

Video encoded as H.264 needs an even width and height, so switch on even numbers when the size is for a video export.

Divide the width and height by the largest number that divides both. 1920 and 1080 both divide by 120, giving 16:9.

1280 × 720, 1920 × 1080, 2560 × 1440 and 3840 × 2160 are the common ones.

9:16, vertical full screen. 1080 × 1920 is the usual export size.

H.264 video needs an even width and height, so an odd size fails to export or gets trimmed. Images don't need it.

No. When you read a size from a file, your browser only reads its width and height. Nothing is sent anywhere.