Aspect Ratio Calculator
Find the aspect ratio of any screen, image or video size, and work out the matching height or width when you resize it.
New size
1,280 × 720
- Aspect ratio
- 16:9
- As a decimal
- 1.7778 : 1
1,920 × 1,080 is 16:9. Keeping that shape, a width of 1,280 needs a height of 720.
How it's worked out
- Simplify
1920 : 1080, divided by 12016:9 - New height
1,280 × 1,080 ÷ 1,920720
Common sizes
| Name | Size | Ratio |
|---|---|---|
| HD | 1280 × 720 | 16:9 |
| Full HD | 1920 × 1080 | 16:9 |
| 4K UHD | 3840 × 2160 | 16:9 |
| Instagram portrait | 1080 × 1350 | 4:5 |
| Story or Reel | 1080 × 1920 | 9:16 |
| Square | 1080 × 1080 | 1:1 |
The formulas
Ratio = width ÷ gcd : height ÷ gcd · New height = new width × H ÷ W
Example
1920 × 1080 simplifies to 16:9, which is 1.778 : 1. Scaled to 1280 wide, it becomes 1280 × 720.
Questions people ask
How do I find an aspect ratio?
Divide the width and height by their greatest common divisor. 1920 × 1080 divides by 120 to give 16:9.
How do I resize keeping the ratio?
New height = new width × original height ÷ original width. At 16:9, a 1280 px width needs a 720 px height.
What sizes suit Instagram and Reels?
1080 × 1350 (4:5) for portrait posts, 1080 × 1080 for square and 1080 × 1920 (9:16) for Stories and Reels.
About this calculator
Formula and rules last checked 25 October 2026Written and tested by the CalculatorDex teamReport a problem