Aspect Ratio Calculator
Find the ratio of any width and height, or the missing dimension for a ratio you already have.
An aspect ratio is width divided by height, reduced to whole numbers. 1920 × 1080 is 16:9, because both divide by 120. To find a missing dimension, multiply the known one by the ratio: at 16:9, a 1280 width gives 1280 × 9 ÷ 16 = 720.
By Piero Nanni · Last checked
Find the ratio
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Find the missing dimension
An aspect ratio describes shape, not size. Every resolution in the 16:9 family, from 1280 × 720 up to 3840 × 2160, is the same shape, which is why content scales between them without bars or cropping. Reduce any width and height by their greatest common divisor and you get the ratio.
Mixing ratios is what produces letterboxing and pillarboxing. Put 16:9 video into a 4:3 frame and you get black bars top and bottom; put a 4:3 photo into a 16:9 slide and the bars move to the sides. Nothing is wrong in either case, the shapes simply differ, and the only fixes are cropping or accepting the bars.
Standard aspect ratios
| Ratio | Decimal | Where it is used | Example resolution |
|---|---|---|---|
| 1:1 | 1.000 | Square social posts, profile images | 1080 × 1080 |
| 5:4 | 1.250 | Older monitors, 8 × 10 prints | 1280 × 1024 |
| 4:3 | 1.333 | Classic TV, iPad, many projectors | 1024 × 768 |
| 3:2 | 1.500 | 35 mm film, most DSLR sensors | 3000 × 2000 |
| 16:10 | 1.600 | Laptop and productivity displays | 1920 × 1200 |
| 16:9 | 1.778 | HD and 4K video, most screens | 1920 × 1080 |
| 1.85:1 | 1.850 | Standard cinema widescreen | 1998 × 1080 |
| 2:1 | 2.000 | Univisium, some streaming series | 2048 × 1024 |
| 21:9 | 2.333 | Ultrawide monitors | 2560 × 1080 |
| 2.39:1 | 2.390 | Anamorphic cinema scope | 2048 × 858 |
| 9:16 | 0.563 | Vertical video, stories and reels | 1080 × 1920 |
Common 16:9 resolutions
| Name | Resolution | Megapixels |
|---|---|---|
| nHD | 640 × 360 | 0.23 |
| qHD | 960 × 540 | 0.52 |
| HD (720p) | 1280 × 720 | 0.92 |
| Full HD (1080p) | 1920 × 1080 | 2.07 |
| QHD (1440p) | 2560 × 1440 | 3.69 |
| 4K UHD | 3840 × 2160 | 8.29 |
| 8K UHD | 7680 × 4320 | 33.18 |
Reducing a ratio by hand
Divide both numbers by their greatest common divisor. For 1920 and 1080 that is 120, giving 16 and 9. For 2560 and 1600 it is 320, giving 8:5, which is the same shape as 16:10 and usually written that way by convention.
Some ratios do not reduce to small whole numbers, which is why cinema uses decimal forms like 1.85:1 and 2.39:1. Those are the ratio expressed as a single number against one, and they are exact enough for the purpose even though no tidy integer pair produces them.
Finding a missing dimension
Multiply the dimension you have by the other side of the ratio and divide by its own side. At 16:9 with a width of 1280: 1280 × 9 ÷ 16 = 720. With a height of 900: 900 × 16 ÷ 9 = 1600.
Round carefully. Video encoders often require even numbers, and some require multiples of eight or sixteen, so a mathematically correct 1707 × 960 may need to become 1706 × 960. Rounding the smaller dimension usually distorts less.
Ratio, resolution and pixel density
Aspect ratio says nothing about how many pixels there are. 1280 × 720 and 3840 × 2160 are both 16:9, differing by a factor of nine in pixel count. A design that works at one will lay out identically at the other, and only the detail changes.
It also says nothing about physical size. A 27-inch and a 32-inch monitor can both be 16:9 at 2560 × 1440, in which case the larger one has lower pixel density and looks coarser at the same viewing distance.
Frequently Asked Questions
What aspect ratio is 1920 × 1080?
16:9. Both numbers divide by 120 to give 16 and 9.
What is 16:9 in decimal?
16 ÷ 9 is about 1.778, so a 16:9 frame is 1.778 times wider than it is tall.
How do I find the height for a 16:9 width?
Multiply the width by 9 and divide by 16. A width of 1280 gives a height of 720.
What ratio is vertical video?
9:16, which is 16:9 turned on its side. 1080 × 1920 is the usual resolution.
Why does my video have black bars?
The video and the frame have different aspect ratios. The bars fill the shape difference rather than cropping the picture.