Aspect Ratio Calculator
Enter a ratio and one dimension to compute the matching width or height in pixels — plus the simplified ratio and the common name (HD 16:9, photo 3:2, cinema, ultrawide).
Height for 16:9
1080 px
- Width
- 1920 px
- Height
- 1080 px
- Simplified ratio
- 16:9
- Decimal ratio
- 1.78
- Common name
- HD 16:9
Aspect ratio = width ÷ height. For a 16:9 ratio, height = width × 9 / 16, and width = height × 16 / 9.
How to use this calculator
Set the ratio terms (for example 16 and 9 for HD video, or 4 and 3 for standard TV). Pick whether you already know the width or the height, then enter that value in pixels. The calculator returns the matching dimension along with the simplified ratio and decimal form.
How the calculation works
Aspect ratio is defined as width divided by height. Given a target ratio of w:h and a known width, the matching height is width × h ÷ w; given a known height, the matching width is height × w ÷ h. The simplified ratio is computed by dividing both terms by their greatest common divisor (Euclidean algorithm). A common-name lookup labels the decimal — for example 1.778 lands on HD 16:9, 1.5 on photo 3:2, and 2.333 on ultrawide 21:9 — within a 1% tolerance.
Worked example
A 16:9 HD video at a width of 1920 pixels has a matching height of 1920 × 9 ÷ 16 = 1080 pixels — the familiar 1920 × 1080 Full-HD resolution. Switching to a 4:3 ratio at a height of 600 pixels gives a width of 600 × 4 ÷ 3 = 800 pixels. A 1440 × 900 monitor has a simplified ratio of 1440/gcd × 900/gcd = 8:5 (decimal 1.6), which the calculator labels as Widescreen 16:10.
Frequently asked questions
What aspect ratio should I use for YouTube, Instagram, and TikTok?
YouTube uploads at 16:9 (HD: 1920 × 1080, 4K: 3840 × 2160). Instagram feed posts are 1:1 (square, 1080 × 1080), portraits 4:5 (1080 × 1350), and Stories/Reels 9:16 (1080 × 1920). TikTok uses 9:16 vertical at 1080 × 1920. Set the ratio in the calculator and plug in one dimension to size the other for your target platform.
How is the simplified ratio worked out?
The two ratio terms are divided by their greatest common divisor (GCD). For example 1920 and 1080 share a GCD of 120, so 1920:1080 simplifies to 16:9. The Euclidean algorithm finds the GCD by repeatedly replacing the larger number with the remainder of dividing it by the smaller, until the remainder reaches zero — the same routine used in standard maths libraries.
Why does 1.778 get labelled HD 16:9 — is it not 1.7777...?
The decimal 16 ÷ 9 = 1.777... is what the screen industry rounds to 1.78 or labels 16:9. The common-name lookup matches any decimal within a 1% tolerance of a named ratio, so 1.77, 1.78, and 1.7778 all resolve to HD 16:9. Decimals that do not fall within 1% of any named ratio are labelled "Custom".
Does the aspect ratio depend on the pixel aspect ratio (PAR)?
On modern digital displays, pixels are square (PAR = 1:1), so the display aspect ratio equals the pixel-grid ratio shown by this calculator. Older standards like DV PAL or NTSC anamorphic used non-square pixels — the storage frame was 720 × 576 (PAL) but displayed at 1.46:1 because each pixel was wider than it was tall. For any project using square pixels — which is essentially everything since about 2010 — the numbers here are correct.
What aspect ratio is best for printing photos?
It depends on the print size. 6×4 inch prints are 3:2 (matches most DSLR sensors). 7×5 is 7:5. 10×8 is 5:4 and crops top and bottom of a 3:2 sensor. A4 is roughly √2:1 (1.414). Set the print size in the same units in the calculator (or scale from a target width) to see how much your image will need to be cropped.
How do I handle non-integer ratios like 1.85:1 (cinema)?
Enter 185 and 100 (or 1850 and 1000) as the ratio terms — the calculator handles any positive integers and simplifies the result. The simplified form of 185:100 is 37:20, which still resolves to a decimal of 1.85 and labels as Cinema 1.85:1. The same approach works for anamorphic 2.39:1 (239:100 → 239:100, decimal 2.39).