Aspect Ratio Calculator
Find the simplified aspect ratio of any width and height, or calculate missing dimensions from a known ratio.
Aspect Ratio
Calculate ratio from dimensions or find missing dimensions from a ratio
Table of Contents
About
An aspect ratio describes the proportional relationship between the width and height of an image, screen, or video. It is expressed as two numbers separated by a colon, such as 16:9 or 4:3. The first number represents the width, and the second represents the height. Aspect ratios are essential for resizing images, designing websites, choosing monitors, and creating video content that displays correctly across different devices.
How to Use
The aspect ratio calculator helps you find the proportional relationship between width and height. Select the mode that matches what you need:
- Find Ratio — Enter width and height in pixels. The calculator finds the simplified ratio (e.g., 1920 × 1080 becomes 16:9).
- Find Width — Enter a height and a target aspect ratio to calculate the matching width. The result is rounded to the nearest whole pixel since screen dimensions must be integers.
- Find Height — Enter a width and a target aspect ratio to calculate the matching height. The result is rounded to the nearest whole pixel since screen dimensions must be integers.
Use the preset buttons to quickly apply common aspect ratios like 16:9, 4:3, or 21:9.
How to Calculate
Aspect ratio is found by dividing the width and height by their greatest common divisor (GCD). Enter any two values into the calculator above — it automatically computes the GCD and shows each simplification step in the Solution panel. When the exact simplified ratio doesn't match a common named standard (e.g., 43:18 instead of the industry label 'Ultrawide ~21:9'), the tool displays the precise GCD result — the named ratio is a marketing approximation, not a mathematical exactness.
Simplified Ratio = Width ÷ GCD(Width, Height) : Height ÷ GCD(Width, Height)
Examples
HD Video
A YouTube video is 1920 pixels wide and 1080 pixels tall. The aspect ratio is 16:9, the standard for HD and Full HD content.
Photography Print
A photo measures 2400 pixels by 1800 pixels. Its aspect ratio is 4:3, matching classic photographic prints and art paper sizes.
Ultrawide Gaming
A racing game renders at 3440 × 1440 on an ultrawide monitor. This gives an aspect ratio of roughly 21:9, providing a wider field of view for immersive gameplay.
Smartphone Screen
A modern smartphone has a display resolution of 2532 × 1170 pixels. This works out to approximately 19.5:9, the tall aspect ratio common in today's mobile devices.
Cinema Screen
A movie theater frame measures 2048 × 858 pixels. This works out to approximately 2.39:1, a common anamorphic widescreen format used in feature films.
Building Facade
An architect designs a storefront window that is 3600 mm wide and 2400 mm tall. The aspect ratio is 3:2, a proportion often used in architectural glass panels and retail displays.