Aspect ratio calculator

An aspect ratio calculator for images, screens and video

The aspect ratio of an image is the relationship between its width and its height. This calculator finds it from the pixel dimensions, works out the new height or width when you resize image dimensions without stretching, and shows how to move from one format to another, either by cropping or by adding black bars. A preview to scale draws the rectangles on top of each other. Everything runs in your browser: no image is uploaded.

How to use it

1. Type the "Width (px)" and "Height (px)", or click one of the "Common sizes" (Full HD, vertical story, square post, shared link preview and more). "Rotate" swaps the two values.
2. "1. Find the aspect ratio" shows the "Simplified ratio", the decimal ratio, the closest common format, the megapixel count, the orientation and the print size at 300 dpi.
3. In "2. Resize without distortion", pick the "Proportions to keep" (the image's own, a format from the list or "Other ratio (a:b)"), then type a new width or a new height: the other one is filled in. The "Lock proportions" button acts as the padlock.
4. In "3. Change the format", choose the "Target format", then "Crop" or "Add black bars". Each block has its own "Copy result" button.

What a ratio is and how to simplify it

Divide the width and the height by their greatest common divisor (GCD). For 2560 × 1440, the GCD is 160: 2560 ÷ 160 = 16 and 1440 ÷ 160 = 9, so the screen is 16:9, or 1.778 as a decimal. A 1080 × 1350 image gives 4:5. Some sizes barely simplify: the old 1366 × 768 laptop screen gives 683:384, and the calculator reports the closest common format, 16:9, with the gap as a percentage (anything within 3% counts as close).

Common formats and where you meet them

• 16:9: monitors, TVs, HD, Full HD and 4K video.
• 4:3: older TVs, tablets and most smartphone photos.
• 3:2: DSLR and mirrorless cameras (6000 × 4000) and the classic 4 × 6 in print.
• 1.85:1 and 2.39:1: the two cinema formats, flat widescreen and scope.
• 9:16: vertical videos and stories.
• 1:1 and 4:5: square posts and tall portrait posts; 4:5 is also the 8 × 10 in print.
• 21:9: ultrawide monitors; a 2560 × 1080 "21:9" screen is really 64:27.

Resizing without distortion: the proportion rule

New height = new width × height ÷ width. At 16:9, a width of 1280 gives 1280 × 9 ÷ 16 = 720. At 4:3, a height of 1000 gives a width of 1000 × 4 ÷ 3 = 1333.33 px, rounded to 1333. With "Round to an even number (video)" ticked, the tool takes the nearest even number, 1334, because most video encoders need even dimensions. Unlock the proportions and both fields become free, with the distortion given as a percentage.

Crop or add bars

To turn a 4032 × 3024 phone photo (4:3) into 16:9, cropping keeps the largest 16:9 rectangle that fits inside: 4032 × 2268. That means cutting 378 px at the top and 378 px at the bottom, so 25% of the pixels are lost. The other way round, to show a 1920 × 1080 video in a 4:3 frame without cutting anything, it sits in a 1920 × 1440 frame with 180 px bars at the top and bottom (letterbox). An image narrower than the frame gets bars on the sides instead (pillarbox).

Pixels, megapixels and print size

Megapixels are the total pixel count divided by one million: 1920 × 1080 = 2.07 MP, 6000 × 4000 = 24 MP. For a sharp print, allow 300 dots per inch. A 3000 × 2000 px image therefore prints at 10 × 6.67 in, about 25.4 × 16.9 cm, and a 1800 × 1200 px image is just enough for a 4 × 6 in print.

Frequently asked questions

Is 16:9 the same as 1.78:1?

Yes. 16 ÷ 9 = 1.7778, which is often rounded to 1.78:1. In the "Ratio a:b" field you can type 16:9, 16/9 or a single number such as 2.39.

Why is 1366 × 768 not exactly 16:9?

Because 1366 ÷ 768 = 1.7786, not 1.7778. The difference is invisible.

Is the crop always centred?

The cut is split equally between both sides. When the number of pixels to remove is odd, the extra pixel goes to the bottom or the right.

Are my images sent anywhere?

No. The tool never reads a file, only the numbers you type.