How to use the aspect ratio calculator
- Ratio and resize: pick the units, then type a width and a height. You get the simplified ratio (such as 16:9), the decimal ratio (1.78:1), the nearest common ratio and a small preview of the shape.
- Resize: type a new width, or a new height, under "Resize, keeping the shape". The other side is filled in. In pixels it is rounded to a whole pixel, and the exact figure is shown too.
- Screen size (diagonal): enter a screen's diagonal and its ratio to get its width and height in inches and centimeters, or enter the width and height to get the diagonal.
Using it as a 16:9 calculator: press 16:9 under "Start from a ratio", then type the width you want, such as 1280, in New width. The height comes out as 720.
What is the aspect ratio of 1920x1080?
It is 16:9. An aspect ratio is the width compared with the height, reduced to the smallest whole numbers. To reduce it, divide both sides by their greatest common divisor (GCD), the largest number that divides both exactly:
| Step | 1920 x 1080 | 2560 x 1080 |
|---|---|---|
| Greatest common divisor | 120 | 40 |
| Width / GCD | 1920 / 120 = 16 | 2560 / 40 = 64 |
| Height / GCD | 1080 / 120 = 9 | 1080 / 40 = 27 |
| Simplified ratio | 16:9 | 64:27 |
| Decimal ratio (width / height) | 1.78:1 | 2.37:1 |
The decimal ratio is easier to compare: 1.78:1 is wider than 1.33:1 (4:3) and narrower than 2.39:1. Portrait shapes are shown the other way round too, so 9:16 is 1:1.78.
Some sizes do not reduce neatly. 1366 x 768, a common laptop screen, is 683:384, which is 1.78:1 and only 0.05% wider than 16:9, so it is sold as 16:9. The calculator shows the nearest common ratio and how far off it is.
Resize an image and keep the aspect ratio
To keep the shape, scale both sides by the same amount. For a new width: new height = new width x original height / original width. For a new height: new width = new height x original width / original height.
| Original | You enter | Working | New size |
|---|---|---|---|
| 1920 x 1080 px | Width 1280 | 1280 x 1080 / 1920 = 720 | 1280 x 720 px |
| 1920 x 1080 px | Width 1000 | 1000 x 1080 / 1920 = 562.5 | 1000 x 563 px |
| 1024 x 768 px | Height 720 | 720 x 1024 / 768 = 960 | 960 x 720 px |
| 8.5 x 11 in | Width 4 | 4 x 11 / 8.5 = 5.18 | 4 x 5.18 in |
Pixels are whole, so 562.5 becomes 563 and the new picture is a fraction of a pixel off the exact shape. Nobody can see that, but it is why some sizes can never be exactly 16:9. Widths that are multiples of 16 (such as 1280 or 1024) give whole-pixel heights at 16:9.
This calculator gives you the numbers. To resize an actual photo, our sister site's image resizer keeps the shape for you and also works in your browser, without uploading the file.
Screen size from the diagonal
Screens are sold by their diagonal, corner to corner. With the ratio w:h, the sides come from Pythagoras: width = diagonal x w / √(w² + h²) and height = diagonal x h / √(w² + h²). For 16:9, √(16² + 9²) = √337 = 18.358.
| Screen | Width | Height |
|---|---|---|
| 24 in, 16:10 | 20.35 in (51.69 cm) | 12.72 in (32.31 cm) |
| 27 in, 16:9 | 23.53 in (59.77 cm) | 13.24 in (33.62 cm) |
| 55 in, 16:9 | 47.94 in (121.76 cm) | 26.96 in (68.49 cm) |
| 65 in, 16:9 | 56.65 in (143.90 cm) | 31.87 in (80.94 cm) |
Worked example: a 55 inch 16:9 TV is 55 x 16 / 18.358 = 47.94 inches wide and 55 x 9 / 18.358 = 26.96 inches high. Centimeters use the exact inch: NIST states the inch "is exactly equivalent to 25.4 mm", so 1 inch = 2.54 cm. These are the picture's size, not the TV's: add the frame and stand, and note that the advertised diagonal can be rounded.
Common aspect ratios
| Ratio | Decimal | Typical use | Example sizes |
|---|---|---|---|
| 16:9 | 1.78:1 | HD and 4K TV, most monitors, video | 1280 x 720, 1920 x 1080, 3840 x 2160 |
| 16:10 | 1.6:1 | Many laptops and monitors | 1920 x 1200, 2560 x 1600 |
| 4:3 | 1.33:1 | Older TVs and monitors, many phone photos | 1024 x 768, 1600 x 1200 |
| 3:2 | 1.5:1 | 35 mm film (36 x 24 mm), many cameras | 6000 x 4000 |
| 5:4 | 1.25:1 | Older square-ish monitors, 8 x 10 prints | 1280 x 1024 |
| 1:1 | 1:1 | Square posts and profile pictures | 1080 x 1080 |
| 4:5 | 1:1.25 | Portrait posts on social media | 1080 x 1350 |
| 9:16 | 1:1.78 | Vertical phone video and stories | 1080 x 1920 |
| 21:9 | 2.33:1 | Ultrawide monitors (really 64:27 or 43:18) | 2560 x 1080, 3440 x 1440 |
| 2.39:1 | 2.39:1 | Widescreen cinema | Letterboxed films |
16:9 is set in the international standards for HDTV and UHDTV. ITU-R Recommendation BT.709 lists "Aspect ratio" 16:9 with 1 920 samples per active line and 1 080 active lines. BT.2020 gives a "Picture aspect ratio" of 16:9 for both 3 840 x 2 160 and 7 680 x 4 320. Both use square pixels, so the pixel counts and the picture have the same shape.
Pixels, inches, centimeters or feet
A ratio has no units: 16 by 9 inches, 16 by 9 feet and 1920 by 1080 pixels are all 16:9, so this aspect ratio calculator works in pixels, inches, centimeters or feet. Only rounding changes: pixels are rounded to whole numbers, other units to two decimal places. Sides with decimals are scaled up first, so 13.5 x 9 inches is 135:90, which reduces to 3:2, and US letter paper, 8.5 x 11 inches, is 17:22.
This tool is for screens, images, paper and frames. A tire's "aspect ratio" (the 55 in 225/55R17) is the sidewall height as a percentage of the tire's width, which is a different thing.
In Excel or Google Sheets
With the width in A2 and the height in B2 (whole numbers), this gives the ratio as text, such as 16:9:
=A2/GCD(A2,B2)&":"&B2/GCD(A2,B2)
GCD "Returns the greatest common divisor of two or more integers" (Microsoft). Both Excel and Google Sheets cut off decimals in GCD, so turn sides like 13.5 into whole numbers first (multiply both sides by 10). For a new width in C2, the height that keeps the shape, to the nearest whole pixel, is =ROUND(C2*B2/A2,0).
Questions and answers
What is the aspect ratio of 1920x1080?
16:9. The greatest common divisor of 1920 and 1080 is 120, and 1920 / 120 = 16, 1080 / 120 = 9. As a decimal it is 1.78:1.
How do I resize an image and keep the aspect ratio?
Multiply the new width by the original height, then divide by the original width. For 1920 x 1080 at 1280 wide: 1280 x 1080 / 1920 = 720, so 1280 x 720.
What aspect ratio is 4K?
4K UHD TV is 3840 x 2160, which is 16:9, the same shape as 1920 x 1080 with twice the width and twice the height.
How wide is a 55 inch 16:9 TV?
The picture is about 47.94 inches (121.76 cm) wide and 26.96 inches (68.49 cm) high. The TV itself is a little larger because of its frame.
Is a 21:9 monitor really 21:9?
Not exactly. 2560 x 1080 is 64:27 (2.37:1) and 3440 x 1440 is 43:18 (2.39:1). 21:9 itself would be 2.33:1. "21:9" is a rounded name for these ultrawide shapes.
What aspect ratio is vertical phone video?
Usually 9:16, such as 1080 x 1920: the 16:9 shape turned on its side.
Sources
Checked on 9 October 2026. If a rule has changed, please tell us.
- ITU-R BT.709: Parameter values for the HDTV standards for production and international programme exchange (table item 2.1, aspect ratio)
- ITU-R BT.2020: Parameter values for ultra-high definition television systems (Table 1, picture spatial characteristics)
- NIST: SI units, length (the inch is exactly 25.4 mm)
- Microsoft Support: GCD function
- Google Docs Editors Help: GCD function
- Microsoft Support: ROUND function