Aspect Ratio Calculator
Known Dimension
px
Width1,280 px
Height720 px
Simplified Ratio16:9
The Aspect Ratio Calculator keeps images and video in proportion when you resize them. Pick a target ratio such as 16:9, type either the new width or the new height, and it solves for the missing dimension so nothing gets stretched or squashed. It also reduces any raw width and height to its lowest whole-number terms using the greatest common divisor, so you can see that 1920x1080 really is 16:9.
Formula
height = width × (ratioH / ratioW); width = height × (ratioW / ratioH)
- ratioW
- Width term of the target ratio (e.g. 16)
- ratioH
- Height term of the target ratio (e.g. 9)
- width
- Known or computed pixel width
- height
- Known or computed pixel height
How it works
- Enter the aspect ratio as two numbers separated by a colon (for example 16:9), or tap a preset such as 4:3 or 21:9.
- Choose whether you know the width or the height, then type that pixel value. The calculator multiplies it by the ratio to find the other side.
- The simplified ratio output divides your width and height by their greatest common divisor so the proportion shows in lowest terms.
Worked example
You need a 16:9 thumbnail that is 1280 pixels wide.
- Ratio terms: ratioW = 16, ratioH = 9.
- Height = 1280 × (9 ÷ 16) = 720.
- Resulting frame is 1280 × 720, which simplifies to 16:9.
Height is 720 px, giving a 1280 × 720 frame at 16:9.
Frequently asked questions
- What does aspect ratio mean?
- Aspect ratio is the proportional relationship between an image width and its height, written as width:height. A 16:9 frame is 16 units wide for every 9 units tall, regardless of the actual pixel count.
- How do I simplify a ratio like 1920:1080?
- Divide both numbers by their greatest common divisor. For 1920 and 1080 the GCD is 120, so the ratio reduces to 16:9. The calculator does this automatically for whole-number inputs.
- Will resizing to a different ratio distort my image?
- If you change the ratio itself the image must be cropped or letterboxed to avoid distortion. This tool preserves the chosen ratio, so scaling one dimension always yields a proportional, undistorted result.
- Can I use decimal dimensions?
- You can enter decimal pixel values and the missing side is computed to two decimal places. Ratio simplification, however, rounds the inputs to whole pixels before finding the greatest common divisor.