What this calculator does
An aspect ratio such as 16:9 describes the proportion between width and height, independent of actual size: a 1920×1080 screen and a 3840×2160 screen are both 16:9, just at different resolutions. This calculator works in both directions, finding a matching dimension for a target ratio, or reducing two dimensions down to their simplest ratio.
Video, photography and screen work all lean on a handful of standard ratios: 16:9 for widescreen video and most monitors, 4:3 for older televisions and some presentation slides, 21:9 for ultrawide displays, and 9:16 for vertical phone video. Getting the ratio wrong is the most common cause of black bars or unwanted cropping when content is resized.
The formula
To find a missing dimension, multiply the known width or height by the target ratio (or its inverse): height = width × (ratio height ÷ ratio width), and the reverse for width. To simplify two dimensions into a ratio, divide both by their greatest common divisor, the largest number that evenly divides them both.
| Term | Meaning |
|---|---|
| Aspect ratio | The proportional relationship between width and height, written as width:height (for example 16:9). |
| GCD | Greatest common divisor: the largest number that divides both dimensions evenly, used to reduce a ratio to its simplest form. |
| Decimal ratio | The aspect ratio expressed as a single number (width ÷ height), such as 1.778 for 16:9. |
The inputs explained
| Field | What to enter |
|---|---|
| Mode | Choose whether to find a missing dimension for a known ratio, or find the ratio between two known dimensions. |
| Aspect ratio (dimension mode only) | A common aspect ratio, or Custom to enter your own. |
| Custom ratio width (if Custom selected) | The width part of a custom ratio, only used when Custom is selected. |
| Custom ratio height (if Custom selected) | The height part of a custom ratio, only used when Custom is selected. |
| Known dimension is | Whether the value you are entering is the width or the height. |
| Known dimension value, or width/height for ratio mode | In dimension mode, the known width or height. In ratio mode, the width. |
| Height (ratio mode only) | Only used in ratio mode: the height, paired with the width above. |
When to use it
Resizing video or an image to a target ratio
Given a fixed width for a video export or thumbnail, finding the matching height for 16:9 (or another target ratio) keeps the frame free of unwanted cropping or letterboxing.
Checking whether a resolution is truly 16:9
Reducing an odd-looking resolution such as 1366×768 down to its simplest ratio (which is not exactly 16:9) explains why some "widescreen" displays crop or stretch content slightly differently from a true 1920×1080 screen.
Planning a print or design layout
Aspect ratio thinking is not limited to screens: a print, poster or social media post has its own target proportions, and the same width-from-height or height-from-width calculation applies.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Matching heights for common video widths at 16:9
A range of common export widths, each paired with the height that keeps a true 16:9 frame.
Questions
What is 16:9 as a decimal?
Dividing 16 by 9 gives approximately 1.778, meaning the width is about 1.78 times the height. This is the standard widescreen ratio used by most modern televisions, monitors and online video.
What resolution is 16:9?
Any resolution where width divided by height equals 16 ÷ 9 works, including 1280×720, 1920×1080 and 3840×2160. All are the same shape at different pixel densities, which is why video exported at any of them fills a 16:9 frame without black bars.
How do I find the ratio between two numbers, like a resolution?
Divide both numbers by their greatest common divisor: for 1920 and 1080, that divisor is 120, giving 16:9. This calculator's ratio mode does that reduction automatically for any pair of dimensions.
Is 1366×768 actually 16:9?
Not exactly. Reducing 1366:768 gives roughly 1.779:1, very close to but not precisely 16:9's 1.778:1, because 1366 does not divide evenly by 16. It is near enough that manufacturers market it as widescreen, but it is not a mathematically exact 16:9 resolution.
For converting between other physical or digital units entirely, browse the unit converters on the site.