Aspect Ratio Calculator
Turn any width and height into a ratio like 16:9, see the closest standard shape, and work out the missing side when you resize.
An aspect ratio is the width and the height, each divided by their greatest common divisor. 1920 and 1080 share 120, so a 1920 by 1080 screen is 16:9, or 1.78:1 as a decimal. To resize without stretching, multiply the new width by the height term and divide by the width term; a 16:9 picture 1280 wide is 1280 x 9 / 16 = 720 high.
Ratios are computed exactly from the numbers you enter; decimals and resized sides are rounded for display, and the rounded whole number is shown next to any side that does not come out whole. The result assumes square pixels.
Resize, keeping the same shape
Pixels, inches or any unit, as long as both sides use the same one. Up to three decimals, sides up to 100,000. You can also type a ratio itself, such as 2.39 and 1.
Aspect ratio
16:9
- As a decimal
- 1.78:1
- Common ratio
- 16:9 exactly
- Orientation
- landscape
- New height
- 720
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About the Aspect Ratio Calculator
Aspect ratio is the shape of a rectangle, written width first. The calculator reduces your two numbers by their greatest common divisor, the method in Book VII of Euclid's Elements, so 3840 by 2160 and 1280 by 720 both come back as 16:9, the HD shape ITU-R Recommendation BT.709 sets with 1920 by 1080 pixels. Not every screen reduces neatly. A 1366 by 768 laptop panel is 683:384 in lowest terms, so the result also names the closest common ratio and the gap: closest to 16:9 (0.05% wider). A 2560 by 1080 monitor is 64:27, sold as 21:9, and the result reads closest to 21:9 (1.59% wider). Turn a frame on its side and the terms swap, so a 1080 by 1920 phone video is 9:16. The resize box keeps the shape: give it a new width and it returns the height, or the reverse. When the answer is not whole, as with a 16:9 frame 1000 wide, it shows 562.50, about 563, and you choose the rounding.
Frequently asked questions
How do I calculate an aspect ratio?+
Find the greatest common divisor of the width and height and divide both by it. For a 1920 by 1080 screen the divisor is 120, giving 16:9. For a decimal form, divide the width by the height: 1920 / 1080 is about 1.78, written 1.78:1.
How do I resize an image without stretching it?+
Keep the width and height in the same ratio. New height equals new width times the height term over the width term, so a 16:9 image resized to 1280 wide becomes 1280 x 9 / 16 = 720 high.
Why does my screen show a ratio like 683:384?+
Some resolutions do not reduce to a familiar pair. 1366 by 768 has a greatest common divisor of only 2, so its lowest terms are 683:384. It sits only 0.05% wider than 16:9, close enough that it is sold as a 16:9 display.
Is 21:9 really 21:9?+
Usually not exactly. Monitors marketed as 21:9 are often 2560 by 1080, which is 64:27, or 3440 by 1440, which is 43:18. Both are a little wider than a true 21:9, and the calculator shows by how much.
Does this work for video with non-square pixels?+
It gives the ratio of the numbers you enter. Some video formats store pixels that are displayed wider or narrower than they are tall, so the picture's shape on screen also depends on that pixel aspect ratio, which this calculator does not apply. For ordinary photos, screens and web images the pixels are square and the result is the shape you see.
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Free to use on your own site. Paste this snippet where you want the aspect ratio calculator to appear — it resizes itself automatically.
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