Free tool
Aspect Ratio Calculator for Images, Video and Layouts
Type a width and a height to see the ratio in its simplest form, drawn to scale. Then scale it to a new size, or find out what it costs to change the shape. You can also read the size of a picture or video file without uploading it.
Resize, keep the shape
Change the shape of your size
Ready sizes for common ratios
This is plain arithmetic in your browser. A file you pick is read only for its dimensions and is never uploaded. Your last numbers are remembered on your own device, and a share link carries them after the hash sign.
The everyday problem: a picture that will not fit the slot
A hero photo arrives at one shape and the layout wants another. A video must be exported at a size that keeps its proportions. A designer needs a banner at three widths, and each height has to follow. All of these are the same sum, and getting it wrong shows up as stretched faces or unexpected black bars.
Start in the first block. Type the width and the height, with or without commas or the letters px, and the calculator shows the ratio reduced to its smallest whole numbers, the decimal form, whether the shape is landscape, portrait or square, and the size in megapixels when the numbers are whole. A small box beside it is drawn to the same proportions, so you can see the shape. If the ratio is close to a well known one, the page names it.
What each block does
| Block | You give it | You get |
|---|---|---|
| Find the ratio | A width and a height, or a file to read | The reduced ratio, the decimal form and a name when it matches a common shape |
| Resize, keep the shape | A ratio and one new side | The other side, with an option to round to even numbers for video |
| Change the shape | Your size and a target ratio | The crop size and how much of the picture it keeps, and the size with bars added instead |
| Ready sizes | Nothing | A table of common ratios at widths from 640 to 3840 |
The file reader takes the dimensions of a picture or video from your computer and fills in the width and height. Nothing is sent anywhere, because only the size is read.
A worked case: widescreen to vertical
Take a frame of 1920 by 1080 pixels. The ratio reduces to 16:9. Now choose a vertical 9:16 target in the shape block. A crop keeps the full height of 1080 and takes a strip about 608 pixels wide from the sides, which is about 32 percent of the original picture. The other option fits the whole frame inside a 9:16 canvas, with bars above and below. The page shows both results, so you can decide whether losing the sides or adding bars suits the content.
Round to even numbers matters for video. Many encoders want both sides divisible by two, so ticking that option nudges a result such as 719 up to 720.
Slips to avoid
- Resizing by changing the width and the height separately. Change one side in the resize block and let the tool work out the other.
- Trusting a rounded ratio. If a size like 1366 by 768 is shown as close to 16:9 but not equal, the page says close to, and not that it is.
- Cropping a face off the edge. Check the share of the picture kept before you commit.
- Forgetting that a ratio only describes shape. 4:5 can be 400 by 500 or 4000 by 5000, so pick a size that suits where the picture is shown.
When a template has to hold many images in one shape, aspect ratio is a layout decision as much as a number. Our landing page structure guide shows how image shapes fit into a page that is built to convert.
Frequently asked questions
How do I find the aspect ratio of an image?
Divide the width and height by their greatest common divisor, or type both into the calculator. For 1920 by 1080 the answer is 16:9.
How do I resize an image without stretching it?
Keep the ratio and change only one side. In the resize block, type the new width and the matching height appears.
Why round to even numbers?
Many video formats and encoders need even pixel counts. The option rounds each side to the nearest even number, and the page shows the exact value it started from.
What happens to a picture when I crop to another ratio?
Part of it is cut away. The calculator gives the cropped size and the percentage of the picture that stays, so you can judge the loss.
Can it read the size of a video file?
Yes, you can choose a picture or video file and the page reads its dimensions. The file is not uploaded.
Does it accept decimals?
Yes, a ratio such as 2.39 by 1 is scaled to whole numbers before it is reduced.
More free tools
- Image cropper: Crop pictures to a free box, a ratio, a social size or a circle, with rotate and straighten.
- image resizer: Resize pictures by pixels or percent with fit, crop or stretch, presets and file type choices.
- PPI calculator: Work out pixels per inch, dot pitch and physical size from a screen's resolution and diagonal.
- Square image maker: Turn pictures into squares by adding a background or cropping, at the pixel size you choose.
- screen resolution checker: See your screen size in real pixels, the pixel ratio, window and page area, and an aspect ratio.