Aspect Ratio Calculator
Reduce a width and height to their simplest ratio, then find the matching height for a new width. This helps size images, video and display layouts.
Runs locally in your browser
Scaled dimensions: 1280 × 720 px
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What is the Aspect Ratio Calculator?
Reduce a width and height to their simplest ratio, then find the matching height for a new width. This helps size images, video and display layouts.
How to use it
- 1Enter original width and height in pixels.
- 2Read the reduced ratio.
- 3Enter a new width to calculate the proportional height.
How it works
The greatest common divisor reduces the integer dimensions. The new height is the target width divided by the original width-to-height ratio.
Scale 1080p
1920 × 1080 reduces to 16:9. At a width of 1280 pixels, the proportional height is 720 pixels.
Limitations & notes
- Scaled height is rounded to a whole pixel.
- A ratio does not indicate image quality or whether upscaling will look sharp.
Frequently asked questions
Why does 1366 x 768 not reduce to 16:9?
1366 x 768 is marketed as 16:9, but its exact ratio is 683:384, about 1.7786, while true 16:9 is 1.7778. Manufacturers rounded the width to a convenient number. Ultrawide screens show the same effect: 2560 x 1080 reduces to 64:27 and 3440 x 1440 to 43:18, even though both are sold as 21:9. This calculator shows the exact reduced fraction and the decimal width-to-height value so you can see such differences.
What aspect ratio should I use for social media images and video?
Common targets are 16:9 for YouTube and landscape video (1920 x 1080), 9:16 for Reels, Shorts and TikTok (1080 x 1920), 1:1 for square posts (1080 x 1080) and 4:5 for portrait Instagram feed posts (1080 x 1350). Platform recommendations change, so check each one's current guidelines. Enter your source size here to see whether it already matches, or how tall it would be at a given width.
How do I calculate the height for a new width by hand?
Divide the new width by the original width-to-height ratio. For a 1920 x 1080 image, the ratio is 1.7778, so a width of 800 gives 800 / 1.7778 = 450 pixels. Equivalently, multiply the new width by original height over original width: 800 x 1080 / 1920 = 450. This tool performs the same calculation and rounds the height to the nearest whole pixel.
What is the difference between 16:10 and 16:9 screens?
A 16:10 display, such as 1920 x 1200 (reduced to 8:5) or 2560 x 1600, is about 11 percent taller than a 16:9 screen of the same width, which gives more vertical room for documents and code. Video mastered at 16:9 shows thin black bars on a 16:10 screen. Many laptops have returned to 16:10, while most TVs and monitors stay 16:9.
Can I enter decimal values or calculate width from a height?
The calculator expects positive whole-number pixel dimensions; decimals show a validation message. Scaling works from a new width only, returning the matching height rounded to a whole pixel. To find a width for a fixed height, multiply the height by the Width / height value shown, for example 720 x 1.7778 = 1280. Note that some video encoders need even dimensions, so adjust a rounded odd height by one pixel.
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