Aspect Ratio Calculator - Find, Simplify & Compare Ratios

How to use this tool

Choose a mode. Pick Find Side, Simplify, or Compare from the tabs.
Enter dimensions. Type your values or select a common preset.
Read the result. The missing dimension, simplified ratio, or comparison is shown instantly.

What Is an Aspect Ratio?

An aspect ratio expresses the proportional relationship between width and height as two numbers separated by a colon. A ratio of 16:9 means the image is 16 units wide for every 9 units tall. Aspect ratios are fundamental in video production, photography, web design, and display hardware.

Common Aspect Ratios

16:9 is the standard for HD and 4K video, computer monitors, and most modern TVs. 4:3 was the standard for analogue TV and many older monitors. 21:9 is used for ultrawide displays and cinematic video. 1:1 (square) is popular on Instagram and other social platforms. 9:16 is the vertical portrait format used for Reels, TikTok, and Stories.

Finding a Missing Dimension

Cross-multiplication makes it straightforward. If you know an image is 16:9 and 1920 px wide, the height is (1920 ÷ 16) × 9 = 1080 px. The tool does this calculation instantly in your browser.

Simplifying a Ratio

Any W×H pair can be simplified by dividing both numbers by their greatest common divisor (GCD). 1920 and 1080 share a GCD of 120, giving 16:9. This is useful when checking whether a crop or thumbnail matches the source aspect ratio.

Photography and print aspect ratios

Ratio	Common use	Example resolution
3:2	Full-frame DSLR / mirrorless cameras	6000 × 4000 px
4:3	Micro Four Thirds cameras; older monitors	4032 × 3024 px
1:1	Square medium-format film; Instagram grid posts	3000 × 3000 px
16:9	HD and 4K video; widescreen monitors	1920 × 1080 px
9:16	Mobile-first vertical video (Reels, TikTok, Stories)	1080 × 1920 px
21:9	Ultrawide monitors; anamorphic cinema	3440 × 1440 px
5:4	Large-format film (4×5 inch); older CRT monitors	1280 × 1024 px
4:5	Portrait posts on Instagram (optimal for feed)	1080 × 1350 px

Frequently asked questions

What is an aspect ratio?

An aspect ratio describes the proportional relationship between the width and height of a rectangle. A 16:9 ratio means the width is 16 units for every 9 units of height. Common examples are HD video (16:9), classic TV (4:3), and smartphone portraits (9:16).

How do I find the height for a given width?

Use the "Find side" mode. Enter your aspect ratio (e.g. 16:9) and the known width. The calculator cross-multiplies: height = (width ÷ ratio width) × ratio height.

How is an aspect ratio simplified?

The tool finds the greatest common divisor (GCD) of the width and height, then divides both by it. For example, 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, giving 16:9.

What does the compare mode do?

Compare mode shows the percentage difference in width and height between two pairs of dimensions, and which pair is wider or taller.