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Aspect Ratio Calculator
Calculate, scale, or compare aspect ratios — three modes, instant live preview.
Enter width and height to calculate ratio
16:9
1.78
4:3
1.33
1:1
1.00
3:2
1.50
21:9
2.33
9:16
0.56
4:5
0.80
2:3
0.67
Calculate, scale, or compare aspect ratios — three modes, instant live preview.
Enter width and height to calculate ratio
16:9
1.78
4:3
1.33
1:1
1.00
3:2
1.50
21:9
2.33
9:16
0.56
4:5
0.80
2:3
0.67
An aspect ratio defines the proportional relationship between a rectangle's width and height. It appears everywhere in modern media: the 16:9 standard governs YouTube videos, HD monitors, and smartphone screens in landscape mode; 4:3 remains common in older displays and photography; 1:1 is the square format Instagram popularised; and cinema-scope formats such as 21:9 deliver immersive widescreen experiences.
In graphic design and photography, choosing the right ratio affects composition, print dimensions, and platform compatibility. When resizing images or video frames, maintaining the original ratio prevents distortion. This tool lets you calculate the simplified ratio from any pixel dimensions, find the missing dimension when scaling, and instantly check whether two different resolutions share the same proportions.
The calculation uses the Euclidean GCD algorithm to reduce any pair of integers to their smallest equivalent form, so 1920×1080 correctly simplifies to 16:9 rather than displaying the raw pixel values.
What is an aspect ratio?
An aspect ratio is the proportional relationship between a rectangle's width and height, expressed as two numbers separated by a colon (e.g. 16:9). It describes shape, not size — a 1920×1080 monitor and a 640×360 video window share the same 16:9 ratio.
Why is 16:9 the standard for video?
The 16:9 ratio was chosen as the HDTV standard in the 1980s because it is a geometric compromise between the 4:3 TV format and the wider cinema formats. It matches the natural field of view of human peripheral vision and allows widescreen films to be displayed with minimal letterboxing.
How do I calculate an aspect ratio from pixel dimensions?
Divide both the width and height by their Greatest Common Divisor (GCD). For 1920×1080: GCD(1920,1080) = 120, so 1920÷120 = 16 and 1080÷120 = 9, giving 16:9. The 'Calculate Ratio' mode does this automatically.
What aspect ratios do social media platforms use?
Instagram square posts use 1:1, portrait posts and Stories use 9:16 (4:5 for feed portraits). Twitter/X headers are 3:1, profile banners 16:9. YouTube thumbnails are 16:9. Facebook covers are 2.7:1 (roughly). LinkedIn banners are approximately 4:1.
How do I scale a resolution while keeping the aspect ratio?
Use the 'Scale from Ratio' mode. Enter the ratio (e.g. 16:9) then provide either the target width or height — the calculator solves the missing dimension. Manually: if you know the width, height = width × (ratio height ÷ ratio width). For 16:9 at 1280px wide: height = 1280 × (9÷16) = 720px.
What is the difference between 16:9 and 16:10?
16:10 (also written 8:5) is slightly taller than 16:9, with a decimal value of 1.600 vs 1.778. It was common on older widescreen laptops and designers prefer it for extra vertical workspace. 16:9 became dominant when television and consumer electronics standardised on HD resolutions like 1280×720 and 1920×1080.
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