Aspect Ratio Calculator
Enter the width and height of an image or video frame in pixels and the calculator gives its exact aspect ratio, worked out with the greatest common divisor: 1920 ร 1080 is exactly 16:9, and 1366 ร 768 is exactly 683:384, which is close to 16:9 but not equal to it. It then resizes to a new width or height without stretching.
The part most calculators skip is adapting a frame to a different shape, such as a landscape video for a vertical 9:16 frame. Fit keeps the whole picture and shows the empty bars in pixels. Fill covers the frame and shows the crop rectangle and how much of the picture it keeps. Ideal geometry and whole-pixel results are shown separately, so you can see when rounding makes a size only approximately the ratio you wanted. It calculates dimensions and guidance only. To resize an image file, use the Image Resizer.
Runs in your browser. Aspect Ratio Calculator processes your input on your own device. Nothing you enter or upload is sent to a server.
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(opens in a new tab)How to use the Aspect Ratio Calculator
- Type the original width and height in pixels, or pick a common size such as 1920 ร 1080. The ratio, its decimal value and its orientation appear straight away.
- To resize, type a new width or a new height. The other size is calculated from the original shape, and the result says whether it is exact or rounded. Select Copy Dimensions to copy it.
- To adapt the frame to another shape, pick a target ratio such as 9:16 (or enter your own), then type a target width or height.
- Switch between Fit and Fill to compare the numbers. The side-by-side illustration shows the bars Fit adds and the part of the picture Fill keeps. Your original dimensions are never changed by this.
- Select Reset to return to the 1920 ร 1080 starting example.
Supported formats: Pixel sizes are whole numbers from 1 to 100000, typed as plain digits. A custom ratio takes positive numbers up to 1000 with a period for decimals and at most 4 decimal places, such as 16, 4.5 or 2.39.
What is an aspect ratio?
An aspect ratio is the proportion between a frame's width and its height, written as width:height. It describes shape, not size. A 1920 ร 1080 frame and a 1280 ร 720 frame are different resolutions but share one aspect ratio, 16:9, so one is an exact scaled copy of the other.
Orientation follows from the ratio. A frame wider than it is tall is landscape, a frame taller than it is wide is portrait, and a frame with equal sides is square. Turning a ratio around turns the frame on its side: 16:9 becomes 9:16.
How to calculate aspect ratio from width and height
Divide both numbers by their greatest common divisor, the largest whole number that divides both without a remainder. What remains is the simplest whole-number ratio, and it is exact.
Full HD
Input
1920 ร 1080
Output
Greatest common divisor 120, so 1920 รท 120 : 1080 รท 120 = 16:9
Vertical Full HD
Input
1080 ร 1920
Output
Greatest common divisor 120, so 9:16
Square
Input
1000 ร 1000
Output
Greatest common divisor 1000, so 1:1
Photograph
Input
3000 ร 2000
Output
Greatest common divisor 1000, so 3:2
A size that only looks like 16:9
Input
1366 ร 768
Output
Greatest common divisor 2, so 683:384. That is about 0.05% off 16:9, so the calculator calls it approximately 16:9, never exactly
How to resize while keeping proportions
To keep the shape when you change one side, scale the other side by the same factor: new height = new width ร original height รท original width. For a 1920 ร 1080 frame resized to 1280 pixels wide, that is 1280 ร 1080 รท 1920 = 720, so the result is exactly 1280 ร 720.
Image sizes are whole pixels, so the answer is sometimes not a whole number. Resizing 1920 ร 1080 to 1000 pixels wide gives an ideal height of 562.5. The calculator rounds to the nearest whole pixel (halves round up), so the result is 1000 ร 563, and it tells you that 1000 ร 563 is approximately 16:9 and not exactly. Video encoders often need even sizes, so Even pixels rounds the calculated side to the nearest even number instead, giving 1000 ร 562.
This calculator only supplies the numbers. To resize an actual image, enter them in the Image Resizer, which keeps the aspect ratio locked by default.
16:9 versus 9:16
16:9 is the common landscape shape for video and screens. 9:16 is the same ratio turned on its side, the shape of a phone held upright. At 16:9 the height is the width ร 9 รท 16, which is a whole number only when the width is a multiple of 16.
| Name | 16:9 landscape | 9:16 portrait |
|---|---|---|
| HD | 1280 ร 720 | 720 ร 1280 |
| Full HD | 1920 ร 1080 | 1080 ร 1920 |
| QHD | 2560 ร 1440 | 1440 ร 2560 |
| 4K UHD | 3840 ร 2160 | 2160 ร 3840 |
Fit, Fill and Stretch explained
Moving a picture into a frame with a different shape forces a choice. Fit (also called contain) scales the whole picture until it fits inside the frame, so nothing is lost and the leftover space becomes bars: letterboxing when the bars are above and below, pillarboxing when they are at the sides. The bars are empty space; no new picture is created to fill them.
Fill (also called cover) scales the picture until it covers the whole frame and cuts off what hangs over. The calculator centers that crop. A real editor may need the crop moved to keep a moving subject in view, and no calculator can know where your subject is.
Stretch is neither of these. It scales width and height by different amounts, which squashes or widens everything in the picture. It is shown here only as a warning.
| Measure | Fit | Fill |
|---|---|---|
| Scale | 56.25% of the original | 177.78% of the original |
| Ideal geometry | Content 1080 ร 607.5 | Source crop 607.5 ร 1080 |
| Whole pixels | Content 1080 ร 608, bars 656 above and 656 below (1312 in total) | Source crop 608 ร 1080, starting at x = 656 |
| Picture kept | All of it | 31.64% of the original area |
| Picture removed | None | 68.36% of the original area |
| Shape of the result | Exact frame, with empty bars | Whole-pixel crop is 76:135, approximately 9:16 and not exactly |
Common aspect ratios
These are common conventions, not rules. Platforms and devices change their requirements, so check the current guidance of wherever you will publish.
| Ratio | Orientation | Commonly used for |
|---|---|---|
| 16:9 | Landscape | HD and 4K video, most TVs, monitors and laptops |
| 9:16 | Portrait | Full-screen vertical phone video |
| 1:1 | Square | Square images and video, avatars |
| 4:5 | Portrait | Upright feed images and video |
| 4:3 | Landscape | Older TVs and monitors, many tablets and compact cameras |
| 3:2 | Landscape | 35 mm film and full-frame camera photographs |
| 21:9 | Landscape | Ultrawide displays and widescreen video |
| 2.39:1 | Landscape | Cinema widescreen, entered as a custom ratio |
Common sizes and their exact ratios
Marketing names and exact ratios do not always agree. Several familiar sizes are only close to a standard ratio, which is why the calculator reports the exact ratio first.
| Size | Exact ratio | Standard ratio |
|---|---|---|
| 1280 ร 720 | 16:9 | Exactly 16:9 |
| 1920 ร 1080 | 16:9 | Exactly 16:9 |
| 3840 ร 2160 | 16:9 | Exactly 16:9 |
| 1080 ร 1920 | 9:16 | Exactly 9:16 |
| 1080 ร 1080 | 1:1 | Exactly 1:1 |
| 1080 ร 1350 | 4:5 | Exactly 4:5 |
| 640 ร 480 | 4:3 | Exactly 4:3 |
| 3000 ร 2000 | 3:2 | Exactly 3:2 |
| 1366 ร 768 | 683:384 | Approximately 16:9, not exactly |
| 1920 ร 1200 | 8:5 | No standard ratio within 1% (this is 16:10) |
| 2560 ร 1080 | 64:27 | No standard ratio within 1%; often sold as 21:9 |
| 4096 ร 2160 | 256:135 | No standard ratio within 1% |
- A size is called approximately a standard ratio only when its shape is within 1% of it. Anything further away is shown as its own exact ratio.
Repurposing landscape video for vertical formats
A 1920 ร 1080 landscape frame has a very different shape from a 1080 ร 1920 vertical one, so something has to give. There are three honest options, and the calculator shows the numbers for the first two.
- Fit keeps every pixel but the picture shrinks to 1080 ร 608 and 1312 pixels of the 1920-pixel-tall frame are empty bars. Nothing is generated to fill them.
- Fill covers the whole frame but keeps only a 608 ร 1080 slice of the original, 31.64% of its area. Everything outside it is lost, and the slice is enlarged to about 178%, which softens the picture.
- Re-frame in an editor: choose where the vertical window sits for each shot, or follow a moving subject. That is editing work this calculator cannot do for you.
Things worth knowing
- It calculates dimensions only. It does not open, resize, crop or convert any image or video, and the illustration is a diagram of the geometry, not a preview of your own picture.
- Pixel sizes are whole numbers from 1 to 100000. Decimals, commas and spaces in a size are rejected rather than guessed.
- A custom ratio takes positive numbers up to 1000 with a period for decimals and at most 4 decimal places.
- The Fill crop is always centered. It cannot know where your subject is, so you may need to move it in an editor.
- The rounding choice applies to calculated sizes in the resize and target-frame sections. The whole-pixel figures for Fit and Fill always use the nearest pixel.
- Sizes are treated as square pixels. Anamorphic footage with non-square pixels should be entered at its displayed size.
Frequently asked questions
What aspect ratio is 1920 ร 1080?
Exactly 16:9. The greatest common divisor of 1920 and 1080 is 120, and 1920 รท 120 = 16 and 1080 รท 120 = 9. The decimal ratio is 1.7778 (rounded), width divided by height.
What resolution is 16:9?
Any size where the width is 16 parts to every 9 parts of height. Common examples are 1280 ร 720, 1920 ร 1080, 2560 ร 1440 and 3840 ร 2160. For a given width, the height is the width ร 9 รท 16, which is a whole number only when the width is a multiple of 16, so a width such as 854 gives 480.375 and cannot be exactly 16:9.
How do I calculate an image's aspect ratio?
Divide the width and the height by their greatest common divisor. For 3000 ร 2000 the divisor is 1000, so the ratio is 3:2. Type the two sizes into the calculator and it does this for you and tells you whether the result is exact.
How can I resize to 1280 pixels wide without stretching?
Scale the height by the same factor: new height = 1280 ร original height รท original width. For a 1920 ร 1080 original that is 720, so 1280 ร 720. Type 1280 in New width to see it. To resize the actual file, use the Image Resizer and keep Maintain aspect ratio on.
How do I change 16:9 to 9:16?
Turning a 1920 ร 1080 picture into a 1080 ร 1920 frame cannot be done by resizing alone, because the shape is different. You either Fit it, which keeps everything at 1080 ร 608 with bars above and below, or Fill it, which crops to a 608 ร 1080 slice. Stretching would also fill the frame but distorts the picture.
Can I convert landscape video to vertical without cropping?
Yes, with Fit. The whole landscape picture is kept, but it becomes small and the rest of the vertical frame is empty bars (1312 pixels of bars for 1920 ร 1080 in a 1080 ร 1920 frame). A fuller vertical picture needs cropping or re-framing, because a landscape picture contains no extra image to fill the space.
What is the difference between Fit and Fill?
Fit scales the picture down until all of it fits inside the frame and leaves bars. Fill scales the picture up until it covers the frame and crops the overflow. Fit loses no picture but leaves empty space. Fill leaves no empty space but loses part of the picture.
Why is 1366 ร 768 not exactly 16:9?
Because 1366 ร 9 = 12294 and 768 ร 16 = 12288, and the two would have to be equal. The exact ratio is 683:384, which is about 0.05% from 16:9. It is close enough to be sold as 16:9, so the calculator calls it approximately 16:9 and keeps the exact ratio alongside.
Why does a calculated size say it is approximate?
Pixels are whole numbers, and the other side of a resized frame is often not. 1920 ร 1080 resized to 1000 pixels wide needs a height of 562.5, which becomes 563, so 1000 ร 563 is approximately 16:9 and not exactly. The calculator says so and shows how far the shape moved.
What does Even pixels mean?
Many video encoders need both sides to be even numbers. With Even pixels selected, the calculated side is rounded to the nearest even number instead of the nearest whole number. A side you type yourself is kept as you typed it, and the calculator notes when it is odd.
Is anything I enter sent to a server?
No. All the calculation happens in your browser, and nothing you enter is sent anywhere.