Quick answer
The aspect ratio is width ÷ g : height ÷ g with g = gcd(width, height). 1920 × 1080 has g = 120 and an aspect ratio of 16:9, or 1.7778 as a decimal.
Enter a width and height. The calculator returns the simplified ratio and the decimal ratio.
Related tools: 16:9 Aspect Ratio Calculator: The missing dimension for a 16:9 frame. Resolution Scale Calculator: Scaled resolution at a percentage. Screen Size Calculator: Width, height and area of a screen from its diagonal and aspect ratio.
How to use the Aspect Ratio Calculator
- Enter width (above 0).
- Enter height (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Width | A number | > 0 |
| Height | A number | > 0 |
Formula and method
Formula
ratio = width ÷ g : height ÷ g, g = gcd(width, height)
IEEE-754 double precision; shown to the decimals indicated.
Whole-number pixel sizes give an exact ratio.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Width = 1920; Height = 1080.
| Result | Value |
|---|---|
| Aspect ratio | 16:9 |
| Decimal ratio | 1.7778 |
Example 2
Inputs: Width = 1024; Height = 768.
| Result | Value |
|---|---|
| Aspect ratio | 4:3 |
| Decimal ratio | 1.3333 |
Example 3
Inputs: Width = 3440; Height = 1440.
| Result | Value |
|---|---|
| Aspect ratio | 43:18 |
| Decimal ratio | 2.3889 |
The first line is the headline result (aspect ratio). Below it the aspect Ratio Calculator lists decimal ratio, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Worked example
gcd(1920, 1080) = 120, so 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9. A 1440 × 1080 image is 4:3, and 2560 × 1080 is 64:27, marketed as 21:9.
Rounding
Non-integer sizes are rounded for the ratio. Cropping or letterboxing is needed to display one ratio on another. Photos are often 3:2, phones 9:16 portrait and cinema 2.39:1.
How the result changes with width
Holding every other input at the first worked example, this table changes only width. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Width | Aspect ratio | Decimal ratio |
|---|---|---|
| 960 | 8:9 | 0.8889 |
| 1920 | 16:9 | 1.7778 |
| 3840 | 32:9 | 3.5556 |
| 7680 | 64:9 | 7.1111 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Width: entering "0" shows "Width must be greater than 0." beside that field and no result.
- Height: left empty shows "Enter height." beside that field and no result.
Choosing between the Aspect Ratio Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [16:9 Aspect Ratio Calculator](/technology/16-9-aspect-ratio/) | Matching size | |
| [Resolution Scale Calculator](/technology/resolution-scale/) | width, height and scale | Scaled resolution |
| [Screen Size Calculator](/technology/screen-size-calculator/) | diagonal, aspect ratio width and aspect ratio height | Screen size |
| [TV Mounting Height Calculator](/technology/tv-mounting-height/) | screen diagonal, aspect ratio width and aspect ratio height | Bottom edge height |
| [TV Height Calculator](/technology/tv-height-calculator/) | screen diagonal, aspect ratio width and aspect ratio height | Screen height |
Background: networking and display
Network speeds are quoted in bits per second and file sizes in bytes, and a byte is 8 bits, so a 100 Mbps link moves at most 12.5 megabytes per second; real throughput is usually below the advertised rate. Pixel density is the diagonal in pixels divided by the diagonal in inches: a 1920×1080 display of 24 inches is about 92 pixels per inch, and a 3840×2160 display of 27 inches about 163.
Assumptions and limitations
- Non-integer sizes are rounded for the ratio
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for width and height to confirm this.
Frequently asked questions
What is 4:3 as a decimal?
4:3 is 4 ÷ 3 = 1.3333 as a decimal.
What ratio is 1000 × 1000?
A 1000 × 1000 image has gcd 1000, so the ratio is 1:1, a square.
How do I resize keeping the ratio?
Scale both sides by the same factor.
What does the Aspect Ratio Calculator calculate?
Simplest aspect ratio of a width and height. It returns Aspect ratio and Decimal ratio.
What formula does the Aspect Ratio Calculator use?
ratio = width ÷ g : height ÷ g, g = gcd(width, height). Whole-number pixel sizes give an exact ratio.
What do I need to enter in the aspect Ratio Calculator?
You enter Width and Height.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Non-integer sizes are rounded for the ratio.
What is an example of a aspect Ratio result?
With width 1920 and height 1080, the aspect ratio is 16:9.
Related calculators
- 16:9 Aspect Ratio Calculator — The missing dimension for a 16:9 frame.
- Resolution Scale Calculator — Scaled resolution at a percentage.
- Screen Size Calculator — Width, height and area of a screen from its diagonal and aspect ratio.
- TV Mounting Height Calculator — Bottom and top edge height to center the screen at eye level.
- TV Height Calculator — Screen height from diagonal and aspect ratio.
- TV Viewing Distance Calculator — Viewing distance for a chosen horizontal viewing angle.
- URL Encode/Decode — Percent-encode text for a URL or decode it.
- Image Resolution Calculator — Megapixels and print size of an image.
- eDPI Calculator — Effective DPI from mouse DPI and in-game sensitivity.
Sources
- OpenStax, Prealgebra 2e (Rice University): fractions, decimals, percents, ratios and rounding
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.