Aspect ratio calculator
Find the ratio of a width and height, or work out the missing side of a resize so nothing gets stretched.
Runs entirely in your browser
Find the ratio
- Ratio
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- Decimal
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Resize keeping the ratio
New size -
Type a new width or a new height; the other side is worked out.
Sizes up to 1,000,000 with up to 3 decimal places. Results for the missing side are rounded to whole pixels, with the exact value shown.
How to calculate an aspect ratio
- Type a width and height, such as 1920 and 1080, to see the ratio in its simplest form and as a decimal.
- To resize, pick a ratio (or use the one you just found) and type the new width or the new height.
- Read the other side. If it isn't a whole number, the rounded pixel size and the exact value are both shown.
Aspect ratios in plain numbers
An aspect ratio is the shape of a rectangle: its width compared with its height. It says nothing about size, so 1280 × 720, 1920 × 1080 and 3840 × 2160 are all the same 16:9 shape. To reduce a size to its ratio, divide both sides by the largest number that divides them evenly.
To resize while keeping the shape, multiply or divide by the ratio: new height = new width × ratio height ÷ ratio width, and new width = new height × ratio width ÷ ratio height. If you change only one side without the other, the picture is stretched or squashed.
When the shapes don't match, for example a 4:3 photo in a 16:9 frame, you have three choices: crop the picture to the new shape, fit it inside with bars at the sides, or stretch it. Cropping or fitting keeps things looking right; stretching rarely does.
Tips
- Change an image's pixel size with Resize image, keeping the ratio you worked out here.
- Cut a picture to a new shape, such as square or 16:9, with Crop image.
- Need a percentage scale instead? The percentage calculator shows the sum.
Questions
How is the aspect ratio worked out?
The width and height are divided by their greatest common divisor. For 1920 × 1080 that divisor is 120, so the ratio is 16:9. The decimal form, width ÷ height, is 1.778 to three places, often written 1.78:1.
Why does my 21:9 monitor show 64:27?
"21:9" is a marketing name rather than an exact ratio. A 2560 × 1080 screen is exactly 64:27 (about 2.37:1) and a 3440 × 1440 screen is 43:18 (about 2.39:1), while a true 21:9 would be 2.33:1. The calculator gives the exact figure and notes the name it is sold under.
How do I resize without stretching?
Keep the ratio and work out the missing side: new height = new width × height ÷ width. For 16:9 at a height of 720, the width is 720 × 16 ÷ 9 = 1280. Enter one side in the resize section and the other is filled in.
Why is the result rounded?
Pixels come in whole numbers, so a size such as 1066.67 can't be made exactly. The calculator rounds to the nearest pixel and shows the exact value, so you can see how far off the rounded size is. Picking a width that divides evenly, such as a multiple of 16 for 16:9, avoids rounding.
Which ratio should I use?
16:9 is the standard for HD and 4K video, TV and most laptop screens. 4:3 suits older screens, tablets and many presentation templates. 1:1 is square, 9:16 is full-screen vertical video on phones, 4:5 is a common portrait size for social posts, and 3:2 is the shape of most camera sensors.