How to use the aspect ratio calculator
- Pick Find the aspect ratio to learn the shape of a size, or Find a new width or height to resize while keeping the shape.
- Enter the width and height of your image, video, screen or print. Pixels, inches or any unit works, as long as both use the same one.
- To resize, fill in either the new width or the new height and leave the other blank.
- Read the simplified ratio, the decimal form, the new dimension and the table of the same ratio at common widths.
- Use Copy result, CSV or Print to keep the numbers.
Formula
ratio = width : height, divided by their greatest common divisor
new height = new width x height / width
new width = new height x width / height
Keeping the same ratio means the width divided by the height stays constant. The table of common widths uses the same new height formula. Results are rounded half up to two decimals.
Full HD video scaled to 1280 wide
A frame 1920 wide and 1080 high has a greatest common divisor of 120, so the ratio is 16 : 9 (1920 / 120 = 16 and 1080 / 120 = 9). Width divided by height is 1.7778.
To scale it to 1280 wide, new height = 1280 x 1080 / 1920 = 720. To scale a 1500 by 1000 image to 1000 wide, the height is 1000 x 1000 / 1500 = 666.67, which rounds to 667 pixels. A 1024 by 768 screen is 4 : 3.
What an aspect ratio tells you
An aspect ratio describes shape, not size. Two images that are 16 : 9 can be 640 by 360 or 3840 by 2160, and they will look the same shape on a screen. The ratio is written as width : height, so a wider-than-tall picture has a first number larger than the second. When you resize without keeping the ratio, the image stretches or squashes.
Familiar ratios have names: 1 : 1 is square, 4 : 3 is classic television and many older monitors, 3 : 2 is the shape of 35 mm film frames, 16 : 9 is the shape of most video and monitors, and 21 : 9 is ultrawide. When your size matches one exactly, the calculator names it. Vertical video flips the pair, so 9 : 16.
Resizing without stretching
To scale a picture, multiply both sides by the same factor. If you only know the new width, the new height is the new width times the original height divided by the original width. Because pixel sizes must be whole numbers, the exact answer is rounded. The tool shows both the two-decimal result and the whole-number version, such as 666.67 and 667, so you can see how far the rounding moves the shape. A change of a pixel is far too small to notice in practice.
When the new size has a different ratio than the old one, you must crop or add padding. The crop image and image resizer tools handle that.
Limits
Decimals such as 8.5 by 11 are allowed, and 8.5 : 11 simplifies to 17 : 22. Inputs with more than six decimal places are shown as a decimal ratio instead of a simplified one. The calculator does not account for pixel density, bleed or safe areas. Your numbers stay in this tab.
Assumptions and limits
- Width and height use the same unit, and both must be greater than zero.
- Ratios are simplified using the greatest common divisor of the numbers as entered, with up to six decimal places.
- Resized dimensions are rounded half up to two decimals, and the whole-number version rounds to the nearest pixel.
- A named ratio such as 16:9 is shown only when the simplified numbers match exactly.
Frequently asked questions
How do I calculate the aspect ratio of an image?
Divide the width and height by their greatest common divisor. For 1920 by 1080 the divisor is 120, which gives 16 : 9. This calculator does that for you and also shows width divided by height as a decimal.
How do I resize an image and keep the same proportions?
Choose Find a new width or height, enter the original size and the one new value you know. The other value is the new one times the original other side, divided by the original matching side.
What is 16:9 at 1280 pixels wide?
The height is 720 pixels, because 1280 x 9 / 16 = 720. The table in the results also lists the heights at 320, 640, 1920, 2560 and 3840 pixels wide for the same ratio.
Why is the new height not a whole number?
Most sizes do not divide evenly. A 1500 by 1000 image scaled to 1000 wide would be 666.67 high, so the tool shows the rounded 667 for real pixels and keeps the exact value so you can judge the difference.
What is the difference between 16:9 and 16:10?
A 16:10 frame is taller for the same width. At 1920 wide, 16:9 is 1080 high while 16:10 is 1200 high. Enter 1920 and 1200 to see the ratio simplify to 8:5, which is the same as 16:10.