How to calculate an aspect ratio
An aspect ratio represents the proportional relationship between a shape's width and height. To find the simplified ratio for integer pixel dimensions (like 1920×1080), divide both numbers by their Greatest Common Divisor (GCD):
Width Ratio = Width ÷ GCD(Width, Height) Height Ratio = Height ÷ GCD(Width, Height) Example: 1920×1080 Pixels GCD(1920, 1080) = 120 1920 ÷ 120 = 16 | 1080 ÷ 120 = 9 Result: 16:9 If you are working with reducing large numbers or factoring equations, you can check greatest common divisors directly with our GCF & LCM Calculator.
Standard Aspect Ratios Reference Table
Depending on whether you are designing web layouts, editing digital video, or preparing images for social media, target dimensions fall into well-defined aspect ratio standards:
| Aspect Ratio | Common Resolution | Decimal | Primary Use Cases |
|---|---|---|---|
| 16:9 | 1920×1080 (FHD), 3840×2160 (4K) | 1.77:1 | Modern TVs, computer monitors, YouTube video, landscape posts |
| 9:16 | 1080×1920 | 0.56:1 | Vertical video, TikTok, Instagram Stories, YouTube Shorts |
| 4:3 | 1024×768, 1440×1080 | 1.33:1 | Legacy TVs, retro gaming, iPad screens, photography |
| 1:1 | 1080×1080 | 1.00:1 | Square social media profile pictures and post grids |
| 21:9 (43:18) | 3440×1440, 2560×1080 | 2.38:1 | Ultrawide desktop monitors, cinematic widescreen films |
| 3:2 | 3000×2000 | 1.50:1 | 35mm photography, Microsoft Surface displays |
Why real-world measurements differ from exact ratios
Physical screen sizes and camera sensors rarely hit round whole-number ratios when measured in physical inches or centimeters. Additionally, marketing names often simplify true mathematical proportions.
For instance, a standard 3440×1440 ultrawide monitor is marketed as "21:9". However, dividing 3440 by 1440 simplifies mathematically to 43:18 (or ~2.388:1), which is roughly 2.4% wider than a true mathematical 21:9 ratio (2.333:1). This generator accounts for those small tolerances, reporting both the exact mathematical fraction and the nearest industry name.
Matching image dimensions to physical screens
Knowing the aspect ratio is only half the equation when designing or setting up display hardware. To calculate physical screen dimensions (width and height in inches) from a diagonal measurement, visit our Screen Size Calculator. If you are setting up a home theater, combine your aspect ratio with our TV Size & Viewing Distance Calculator to optimize your room setup.
Frequently asked questions
How do I calculate an aspect ratio from width and height?
Enter the width and height above in any unit. For whole-number dimensions like pixels, you'll get the exact simplified ratio (like 16:9). For decimal measurements, you'll get the decimal ratio plus the closest standard name if one is close.
What ratio is 1920x1080?
1920x1080 is a standard 16:9 widescreen aspect ratio, used by most HDTVs, desktop displays, and online video streaming platforms.
Does changing units (pixels, inches, cm) alter the aspect ratio result?
No. Aspect ratio is a unitless proportion between width and height. Measuring a screen as 1920x1080 pixels or 19.2x10.8 inches yields the exact same 16:9 proportional outcome.
How do I calculate pixel density or image sharpess?
To determine how sharp an image or display looks based on its pixel resolution and physical size, use our PPI (Pixels Per Inch) Calculator.