This aspect ratio calculator finds the ratio of any width and height, such as 16:9, 21:9 or 9:16, and resizes it to a new width or height without stretching. As a screen aspect ratio calculator it works in pixels for monitors, images and video, and in inches or centimeters for prints and frames. It also tells you when a size is sold under a rounder name than its true ratio, lists exact sizes near the one you want, rounds to even numbers for video encoders, and previews how the picture fits on a TV, an ultrawide monitor or a phone, with the black bars that leaves.
How to use the aspect ratio calculator
- Type the width and height, or press a common ratio such as 16:9 or 9:16 to load a typical size.
- Read the Aspect ratio, its decimal value and the shape.
- To resize, type a new width or a new height under Resize, keeping the ratio. The other side fills in.
- Choose how to round: Whole pixels, Even numbers for video, multiples of 8 or 16, or Exact for inches and centimeters.
- Pick a screen under Show it on a screen to see how the picture fits and how much of the screen it uses.
- Use Swap to turn landscape into portrait, and Copy results to save a summary.
What the results mean
| Result | What it tells you | Example: 1920 × 1080 |
|---|---|---|
| Aspect ratio | Width to height in the lowest whole numbers | 16:9 |
| Decimal | Width divided by height | 1.778 : 1 |
| Shape | Landscape, portrait or square | Landscape |
| Pixels | Total pixels, when the size is in pixels | 2.07 MP |
| On the screen | How much of the chosen screen the picture fills without cropping | 75% of a 21:9 ultrawide |
| Exact sizes | Whole number sizes that keep the ratio perfectly | 1264 × 711, 1280 × 720, 1296 × 729 |
How to calculate an aspect ratio by hand
- Find the greatest common divisor of the width and height. For 1920 and 1080 it is 120.
- Divide both by it: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the ratio is 16:9.
- To resize, keep the same proportion: new height = new width × height ÷ width. At 1280 wide, 1280 × 1080 ÷ 1920 = 720.
The same steps give 4:3 for 1024 × 768 and 16:10 for 1920 × 1200. When the numbers do not reduce neatly, the decimal value is easier to compare, for example 2.39:1 for wide cinema films.
Why 21:9 monitors are not exactly 21:9
Ultrawide monitors are sold as 21:9, but none of the common sizes are exactly that:
| Resolution | True ratio | Decimal |
|---|---|---|
| 2560 × 1080 | 64:27 | 2.37 |
| 3440 × 1440 | 43:18 | 2.39 |
| 3840 × 1600 | 12:5 | 2.40 |
| 5120 × 2160 | 64:27 | 2.37 |
True 21:9 would be 2.33. The real sizes sit closer to the 2.39:1 used by wide cinema films, which is why those films fill an ultrawide almost edge to edge. The calculator shows the true ratio and adds Sold as 21:9 when it recognizes the marketing name. To compare the physical size of an ultrawide with a normal screen, use the monitor size calculator.
Phone screens and vertical video
Most phone screens are taller than 16:9. Recent iPhones are about 19.5:9 and many Android phones are 20:9. Vertical video for Reels, TikTok, Shorts and Stories is 9:16 at 1080 × 1920, so on a phone it shows with a thin bar or gets cropped a little at the top and bottom. Portrait posts on Instagram and Facebook use 4:5 at 1080 × 1350, and square posts 1:1 at 1080 × 1080.
Black bars, cropping and fitting
When a picture's ratio differs from the screen's, there are two choices. Fit shows everything and adds black bars: on the top and bottom when the picture is wider than the screen (letterbox), or at the sides when it is narrower (pillarbox). Fill zooms in until the bars disappear and crops the edges instead.
| Picture | Screen | Fit result |
|---|---|---|
| 16:9 video | 21:9 ultrawide | Bars at the sides, 75% of the width used |
| 2.39:1 film | 16:9 TV | Bars top and bottom, 74% of the height used |
| 4:3 video | 16:9 TV | Bars at the sides, 75% of the width used |
| 9:16 video | 16:9 monitor | Bars at the sides, 32% of the width used |
Rounding for video and images
Most video encoders need even numbers for width and height, because they store color at half resolution. Pick Even and the calculator rounds the computed side to the nearest even number. Some older hardware and codecs work best with multiples of 8 or 16. If an exact match matters, use one of the Exact sizes the calculator lists, which keep the ratio without any rounding. To check what your webcam really records, run the webcam resolution test, and to see your display's own size, the screen resolution test.
What an aspect ratio calculator cannot tell you
The calculator assumes square pixels. Some video, such as DVDs at 720 × 480, uses non-square pixels and is stretched on playback, so its stored size gives the wrong ratio. A ratio also says nothing about sharpness: 1280 × 720 and 3840 × 2160 are both 16:9. For pixel density, use the ppi calculator.
Aspect ratio questions
How do I calculate an aspect ratio?
Divide the width and the height by their greatest common divisor. For 1920 × 1080 that is 120, which gives 16:9. To resize, multiply the new width by the height and divide by the width: 1280 × 1080 ÷ 1920 = 720.
What aspect ratio is 1920 × 1080?
16:9, the standard for HD and 4K TVs, most monitors and YouTube. 1280 × 720, 2560 × 1440 and 3840 × 2160 are 16:9 as well.
What is the aspect ratio of an iPhone screen?
Recent iPhones are about 19.5:9. An iPhone 16 has 2556 × 1179 pixels, which works out at 19.51:9. Many Android phones are 20:9, such as 2400 × 1080. Video made for phones is usually 9:16, so it leaves thin bars or is cropped slightly.
What size is a 9:16 video?
1080 × 1920 pixels is the usual size for Reels, TikTok, YouTube Shorts and Stories. 720 × 1280 is the smaller option, and 2160 × 3840 is 4K vertical video.
Is 21:9 the same as 2.39:1?
Close, but not exactly. True 21:9 is 2.33:1. Ultrawide monitors at 2560 × 1080 are 2.37:1 and at 3440 × 1440 are 2.39:1, which matches the 2.39:1 cinema format, so wide films fill them almost perfectly.
What is the aspect ratio of 2560 × 1440?
16:9. It is often called QHD or 1440p, and it has exactly four times the pixels of 1280 × 720.