Aspect Ratio Calculator
Calculate the proportional relationship between width and height, or find a missing dimension from a known aspect ratio.
1. Find Aspect Ratio from Dimensions
Enter pixel, inch, or centimeter dimensions to calculate simplified ratio and decimal fraction.
2. Calculate Missing Dimension
Set your target aspect ratio and input one known side to automatically calculate the proportional missing dimension.
What Is an Aspect Ratio?
An aspect ratio describes the proportional relationship between the width and height of a rectangle, image, video frame, or display screen. It is expressed as two numbers separated by a colon (Width : Height) or as a decimal factor relative to 1.
Unlike absolute physical dimensions measured in centimeters or inches with our online ruler, an aspect ratio represents pure geometry regardless of the screen's physical diagonal or pixel density.
How to Calculate Aspect Ratio
To find the simplified aspect ratio between two pixel dimensions:
- Find the Greatest Common Divisor (GCD) of the width and height using Euclid's algorithm.
- Divide the width by the GCD to find the simplified ratio width.
- Divide the height by the GCD to find the simplified ratio height.
- Divide width by height to get the decimal aspect ratio ($W / H : 1$).
How to Calculate a Missing Width or Height
When resizing images, videos, or responsive web layouts while preserving proportions, calculate the missing dimension using cross-multiplication:
Find Missing Height
Example: With a 16:9 ratio and a width of 1280 px:
Height = 1280 × (9 / 16) = 720 px
Find Missing Width
Example: With a 4:3 ratio and a height of 768 px:
Width = 768 × (4 / 3) = 1024 px
Common Aspect Ratios
Standard proportions widely used in video production, digital photography, and responsive displays:
| Ratio | Decimal | Standard Resolutions | Primary Uses |
|---|---|---|---|
| 16:9 | 1.778:1 | 1920×1080 (FHD), 2560×1440 (2K), 3840×2160 (4K) | Widescreen / HDTV / YouTube standard |
| 9:16 | 0.563:1 | 1080×1920 (TikTok, Reels, Shorts) | Vertical mobile video / TikTok / Reels |
| 1:1 | 1.000:1 | 1080×1080, 2048×2048 (Avatars, Grid) | Square / Profile avatars / Instagram feed |
| 4:3 | 1.333:1 | 1024×768, 1600×1200 (Tablets, CRT) | Classic television / iPad / Photography |
| 3:2 | 1.500:1 | 3000×2000 (Surface Pro), 6000×4000 (DSLR) | 35mm film / DSLR photography / Surface |
| 4:5 | 0.800:1 | 1080×1350 (Social Portrait) | Instagram vertical portrait photo |
| 21:9 | 2.333:1 | 2560×1080, 3440×1440 (Ultrawide Cinema) | Ultrawide monitor / Cinematic 2.39:1 |
Frequently Asked Questions
What is an aspect ratio?
An aspect ratio describes the proportional relationship between the width and height of an image, video, or screen display, written as two numbers separated by a colon (Width:Height).
What does 16:9 mean?
16:9 means that for every 16 units of horizontal width, there are 9 units of vertical height. It is the international standard aspect ratio for high-definition television, YouTube videos, and modern computer monitors.
How do you calculate aspect ratio from pixels?
To calculate an aspect ratio from pixels, divide the width by the Greatest Common Divisor (GCD) of width and height, then divide the height by the same GCD. For example, for 1920 × 1080, the GCD is 120, giving 1920/120 : 1080/120 = 16:9.
How do you find a missing height from a known aspect ratio?
Multiply the known width by the ratio height, then divide by the ratio width: Height = Width × (Ratio Height / Ratio Width). For example, with a 16:9 ratio and a width of 1920 px, Height = 1920 × (9 / 16) = 1080 px.
What is the aspect ratio of 1920 × 1080?
The aspect ratio of 1920 × 1080 is 16:9, which equals approximately 1.7778:1 in decimal notation.