Rescreen / Free tools / Aspect ratio calculator
Aspect ratio calculator
Enter a width and height to get its aspect ratio. Pick a new shape or size to work out the missing side, and see what cropping or letterboxing does to the picture — and to the menus and buttons at its edges. Nothing you enter leaves this page.
How to use the calculator
Enter a size, get its shape, then see what fits where.
Enter your picture
Type the width and height of your video, screen or image. Pixels, inches or any unit work, as long as both match.
Read the ratio
See the ratio in lowest terms, the decimal and the familiar name, such as 16:9, or the nearest one.
Fit it to a frame
Pick a target like 16:9, 9:16, 1:1 or 4:5, or type a missing side, and compare a crop with a letterbox in the preview.
How to calculate an aspect ratio
An aspect ratio is the width divided by the height, written as two whole numbers. To find it, divide both sides by the largest number that goes into both. 1920 and 1080 are both divisible by 120, which gives 16:9. 2560 × 1600 divides by 160 to give 16:10 — strictly 8:5 in lowest terms, but 16:10 is the name everyone uses, so the calculator shows both.
Some sizes do not reduce to a familiar pair. 1366 × 768 is exactly 683:384, which is 1.78:1 — within a fraction of a percent of 16:9, so the calculator says “about 16:9”. Decimals work too: a letter-size page at 8.5 × 11 inches is 17:22.
1920 ÷ 120 = 16 and 1080 ÷ 120 = 9.
Working out the missing width or height
To keep a shape at a new size, multiply by the ratio: height = width × (ratio height ÷ ratio width). A 16:9 picture 1280 pixels wide is 1280 × 9 ÷ 16 = 720 pixels tall. Going the other way, width = height × (ratio width ÷ ratio height).
Why the result is rounded
A pixel cannot be split, so a size that works out at 562.5 has to become 562 or 563. With Even pixels, the calculator rounds to the nearest even number, because H.264 and most other video encoders store colour at half resolution and refuse odd sizes. Whole pixels rounds to the nearest whole number, for images. Exact shows the unrounded figure. Whenever rounding changes a side, the result says what it was before rounding and how far the shape moved — usually well under 0.1%.
Crop or letterbox?
When a picture goes into a frame of a different shape, something has to give. A letterbox keeps the whole picture and fills the leftover space with bars — top and bottom for a wide picture in a taller frame, left and right (pillarbox) for a tall one. A crop fills the frame and cuts off the picture’s edges.
For a film, a crop often works: the subject is usually in the middle. For a screen recording it usually does not, because the things a viewer needs to see — the menu bar, tabs, toolbars, sidebars, the dock — sit at the edges. The preview draws a mock app window so you can see what a crop removes.
Worked example: a laptop screen in a 16:9 video
A 13-inch MacBook Pro screen is 2560 × 1600, which is 16:10. Put it in a 1920 × 1080 (16:9) video and either it is letterboxed — scaled to 1,728 × 1,080with 96-pixel bars at the left and right, leaving 10% of the frame empty — or it is cropped, losing 80 pixels from its top and bottom: 10% of the screen, including the menu bar and probably the dock.
Turning a 1920 × 1080 recording into a 1080 × 1920 vertical video is far harsher. A crop keeps only the middle 32% of the width and throws away 68% of the screen. A letterbox keeps everything but shrinks it to 56% of its size, so text a viewer could read at full width becomes too small on a phone.
Plan the frame before you record
The cheapest fix for a bad crop is to record in the right shape. If the video will be 16:9, record a window sized to 16:9 — 1600 × 900 or 1280 × 720 on a laptop — rather than the whole 16:10 screen. If it will be vertical, use the calculator to size a narrow window (for example 720 × 1280) and keep the controls you click inside it. Make text larger than feels natural: the video will be watched smaller than you recorded it. How to make a tutorial video covers planning and recording a lesson end to end.
Common aspect ratios and sizes
| Used for | Size | Ratio | Decimal |
|---|---|---|---|
| HD video | 1280 × 720 | 16:9 | 1.78:1 |
| Full HD video | 1920 × 1080 | 16:9 | 1.78:1 |
| 1440p video | 2560 × 1440 | 16:9 | 1.78:1 |
| 4K UHD video | 3840 × 2160 | 16:9 | 1.78:1 |
| Vertical video | 1080 × 1920 | 9:16 | 1:1.78 |
| Square post | 1080 × 1080 | 1:1 | 1:1 |
| Portrait feed post | 1080 × 1350 | 4:5 | 1:1.25 |
| Laptop screen | 1440 × 900 | 16:10 | 1.6:1 |
| 13-inch MacBook Pro screen | 2560 × 1600 | 16:10 | 1.6:1 |
| Budget laptop screen | 1366 × 768 | 683:384 (about 16:9) | 1.78:1 |
| Older monitor | 1024 × 768 | 4:3 | 1.33:1 |
| Ultrawide monitor | 2560 × 1080 | 64:27 (about 2.39:1) | 2.37:1 |
| Ultrawide monitor | 3440 × 1440 | 43:18 (about 2.39:1) | 2.39:1 |
“21:9” is a marketing name. Ultrawide monitors are really 64:27 (2560 × 1080) or 43:18 (3440 × 1440), both close to 2.37:1.
Limitations
- It calculates and previews. It does not open, resize, crop or export an image or video file.
- It assumes square pixels, which almost all screens and modern video use. Some older broadcast formats use non-square pixels, and their stored size is not their displayed shape.
- On a high-resolution (Retina) display, the size a screenshot or recording is saved at can be double the “looks like” size in display settings. The ratio is the same either way.
- The crop preview cuts evenly from both edges. An editor can move the crop to one side; the amount lost is the same.
- A platform’s accepted shapes and sizes change. Check its current guidance before you export.
Is anything uploaded?
No. The calculator runs entirely in your browser and has nothing to upload. We count anonymous page views and whether the tool was used; those events never include the sizes you enter. See the privacy policy.
Frequently asked questions
What is the aspect ratio of 1920 × 1080?
16:9, or 1.78:1. So are 1280 × 720, 2560 × 1440 and 3840 × 2160 — they are the same shape at different sizes.
How do I convert 16:9 to 9:16?
Swap the sides: 1920 × 1080 becomes 1080 × 1920. The picture itself has to be cropped or letterboxed to fit, and a crop loses about two thirds of a landscape screen’s width. Pick 9:16 above to see it.
Is 1366 × 768 16:9?
Not exactly. It is 683:384, about 0.05% wider than 16:9, which is close enough that it is sold as 16:9.
Does Rescreen make vertical videos?
No. Rescreen makes 16:9 videos, with your screen fitted inside at its own shape and a background around it, so nothing at the edges is cut off. If you need a vertical version, record a window in that shape.
Does it work on a phone?
Yes. It uses only standard browser features in current Chrome, Edge, Safari and Firefox, and we have tested it in Chrome on desktop and at phone screen sizes.
Spend less time editing
your next recording.
Create an account and record your first video in your browser.