Aspect Ratio Calculator
Enter a width and height to get the aspect ratio, then scale to a new size.
What this tool does
The aspect ratio is the width divided by the height in lowest terms: 1920 × 1080 reduces to 16:9. To resize without distortion, keep the ratio: for a new width of 1280, the height is 1280 × 1080 ÷ 1920 = 720. Enter your size above.
Reduces a width and height to the simplest whole-number ratio using the greatest common divisor.
Finds the new height or width that keeps the same ratio.
How to use it
- Enter the original width and height.
- Choose whether you know the new width or the new height.
- Enter the new value.
- Read the ratio and the matching size.
Why use this calculator
Reduces any width and height to its simplest ratio, names the common formats, and works out the new height for a chosen width (or the new width for a chosen height) without distorting the shape. Stretching a picture or video to fit a space distorts it. Keeping the ratio the same when you resize, crop or pick an upload size avoids black bars and squashed faces.
Why we built it
We built the aspect ratio calculator to reduce a size to its ratio and find the matching height or width, so nothing gets stretched. Resize images with the image size calculator and the ratio calculator.
If your task goes further, try the Golden Ratio Calculator, the Board Foot Calculator and the Tire Size Calculator.
Who this tool is for
- Designers and video editors resizing media
- Photographers cropping to a format
- Web developers setting image sizes
When to use it
- Resizing a photo or video for a website, social post or presentation.
- Choosing a screen or projector format.
- Setting canvas sizes in design tools.
- Checking what shape a resolution is.
How it works
Divide both numbers by their greatest common divisor to get the ratio: 1920 and 1080 share a factor of 120, giving 16:9. To scale, the other side is new value × original other side ÷ original this side.
Common ratios: 16:9 (HD, 4K, YouTube), 4:3 (older TV, many tablets), 3:2 (photography), 1:1 (square posts), 21:9 (ultrawide), 9:16 (vertical video) and 4:5 (portrait posts).
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| Width | 1920 |
| Height | 1080 |
| Scale to a new size by | New width |
| New width or height | 1280 |
With those inputs, the calculator returns:
- Aspect ratio: 16:9
- Decimal ratio: 1.7778
- Commonly used for: widescreen (HD, 4K, YouTube)
- New height: 720
- New size: 1,280 × 720
- Megapixels now: 2.07
What you give it, and what you get back
| Item | Details |
|---|---|
| Width and height | The original size, in any unit. |
| New size | Choose new width or new height, and enter it. |
| Output | Ratio, decimal ratio, common name, the matching size and megapixels. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| The ratio is large, like 683:384 | The size is not a standard shape. | Round to the nearest standard ratio. |
| Decimal sizes | Whole numbers are needed to reduce. | The decimal ratio is shown instead. |
| Result has decimals | The new size does not divide evenly. | Round to whole pixels. |
Assumptions and limitations
- Rectangles only.
- No cropping suggestions - use an image cropper for that.
Frequently asked questions
How do I calculate an aspect ratio?
Divide width and height by their greatest common divisor.
What is the aspect ratio of 1920×1080?
16:9.
How do I resize without distorting?
Keep the ratio: new height = new width × original height ÷ original width.
What aspect ratio is best for YouTube?
16:9 for standard video; 9:16 for Shorts.
What is the aspect ratio of an iPhone screen?
Most recent phones are about 19.5:9, which is a little taller than 9:16.
Is my information sent anywhere?
No. The calculation runs in your browser and nothing leaves the page.
Sources and accuracy
The aspect ratio is width divided by height reduced to its simplest integer form using the greatest common divisor, and scaled sizes preserve that ratio. Common video format ratios such as 16 by 9 are specified in International Telecommunication Union recommendations.
Figures last checked against the source on . Standards and rates can change — if you are relying on this for something that matters, confirm against the source above. Think a figure is wrong or out of date? Send a correction.