Aspect Ratio
Enter a width and height to get the simplified ratio, or type a ratio and a new width to get the matching height. Presets cover video, social and print.
Edit width or height to find the ratio. Edit the ratio to set the height from the width.
| Name | Width | Height | Exact? |
|---|
How the ratio is worked out
An aspect ratio is width divided by height, written as two whole numbers. The tool divides both sides by their greatest common divisor: 1920 × 1080 becomes 16:9 because both are divisible by 120. When the reduced numbers are awkward — 1366 × 768 reduces to 683:384 — it also shows the nearest standard ratio and how far off it is.
To resize, the new height is the new width divided by the decimal ratio (1280 ÷ 1.778 = 720), and the other way round. Tick Round to even numbers for video: most encoders, including H.264, require even dimensions.
Which ratio should I use?
16:9 for YouTube, presentations and most screens. 9:16 for Reels, TikTok and Stories. 4:5 takes up the most space in an Instagram feed; 1:1 is the safe choice for thumbnails and avatars. 3:2 is the native shape of most camera sensors, and A4 paper uses 1:√2, so it keeps its shape when folded in half.
Questions
What is the aspect ratio of 1920 × 1080?
16:9. Both numbers divide by 120, giving 16 and 9. The decimal ratio is about 1.778:1. Other 16:9 sizes include 1280 × 720, 2560 × 1440 and 3840 × 2160 (4K).
How do I calculate height from width and a ratio?
Multiply the width by the second number and divide by the first. For 16:9 at 1280 wide: 1280 × 9 ÷ 16 = 720. Type a new width above and the height fills in automatically.
Is 21:9 really 21:9?
Not usually. “21:9” is a marketing name. Common ultrawide monitors are 2560 × 1080 (64:27, about 2.37:1) or 3440 × 1440 (43:18, about 2.39:1). Enter your exact resolution to see its true ratio.
What size is a 4:5 Instagram post?
1080 × 1350 pixels. Instagram shows portrait posts up to 4:5 in the feed; anything taller is cropped.