16:9 landscape video
16:9 is the widescreen ratio for YouTube, presentations, and most landscape video. 1280×720 is 720p, 1920×1080 is HD, and 3840×2160 is 4K UHD. All three simplify to 16:9. Lock 16:9 when you know only one side of a new export.
Image, video, and CSS ratios
Aspect Ratio Calculator
Type a width and height to simplify the ratio, or lock a ratio and fill one side to calculate the other. For image crops, video frames, and CSS.
Preset sizes in real pixels
These are the frames people actually export. 1920×1080, 1280×720, and 3840×2160 are all 16:9. 1080×1920 is 9:16 for vertical video. 1080×1080 is 1:1, and 1080×1350 is 4:5. Use a row to load those pixels into the calculator.
| Preset | Pixels | Ratio | Used for | Load preset |
|---|---|---|---|---|
| HD 1080p | 1920×1080 | 16:9 | YouTube and landscape video | |
| Vertical HD | 1080×1920 | 9:16 | TikTok, Instagram Reels, YouTube Shorts | |
| Square | 1080×1080 | 1:1 | Instagram square and profile crops | |
| Portrait | 1080×1350 | 4:5 | Instagram feed portrait | |
| HD 720p | 1280×720 | 16:9 | 720p video and lighter exports | |
| 4K UHD | 3840×2160 | 16:9 | 4K masters and large screens |
Scroll the table sideways to see every column.
How to calculate an aspect ratio
Use KeepRatio as an image aspect ratio calculator when you are sizing a crop, or as a video aspect ratio calculator when a timeline needs a matching frame. The same two modes cover both.
01
Find a ratio
Type the pixel width and height. KeepRatio divides both numbers by their greatest common divisor. 1920 and 1080 become 16:9. 1080 and 1350 become 4:5. 1080 and 1080 stay 1:1.
02
Lock a ratio
Choose a ratio such as 16:9 or 9:16, then enter the side you already know. A 16:9 frame that is 1280 pixels wide is 720 pixels tall. A 9:16 frame that is 1080 pixels wide is 1920 pixels tall.
03
Copy the result
Each result has its own copy button: the simplified ratio (16:9), the dimensions (1920×1080), and the CSS declaration (aspect-ratio: 16 / 9;). If a locked size is not a whole pixel, copy the exact size or the nearest whole pixels.
.frame {
width: 100%;
aspect-ratio: 16 / 9;
}Image, video, and social ratios
The pixel presets above are the sizes editors ask for. The notes below say which shape belongs to which job, from a YouTube master to a TikTok cover and a CSS frame.
9:16 vertical video
9:16 is the portrait video ratio used by TikTok, Instagram Reels, and YouTube Shorts. The usual full-HD vertical frame is 1080×1920. It is 1920×1080 turned on its side: same pixel count, opposite ratio.
Instagram 4:5 and 1:1
Instagram feed portraits are often 4:5 at 1080×1350, which gives the photo more room in the grid than a square. Profile crops and square posts are 1:1, commonly 1080×1080. Stories stay on the 9:16 vertical frame.
CSS aspect-ratio
The CSS aspect-ratio property keeps a box in proportion without a padding hack. Copy aspect-ratio: 16 / 9; for widescreen, aspect-ratio: 9 / 16; for a Shorts-style frame, or aspect-ratio: 1 / 1; for a square. The numbers are the same W:H result the calculator shows.
Aspect ratio questions
Short answers for the sizes and ratios this calculator is built around, including 16:9, 9:16, Instagram, TikTok, and YouTube Shorts.
What is an aspect ratio?
An aspect ratio is the proportional relationship between width and height. A 16:9 frame is 16 units wide for every 9 units tall. The units can be pixels or a CSS length. 1920×1080 and 1280×720 are different sizes with the same 16:9 shape.
How does this aspect ratio calculator simplify a ratio?
KeepRatio divides the width and the height by their greatest common divisor, the largest whole number that fits both. 1920 and 1080 share a divisor of 120, so the simplified ratio is 16:9. 1080 and 1350 share a divisor of 270, so the ratio is 4:5.
What is 16:9 in pixels?
16:9 does not lock you to one pixel size. Common 16:9 frames are 1280×720 (720p), 1920×1080 (HD), and 3840×2160 (4K UHD). Multiply a width by 9 and divide by 16 to get the matching height.
What size is 9:16 for TikTok, Reels, and Shorts?
9:16 is the vertical video ratio. A common full-HD vertical frame is 1080×1920, used for TikTok, Instagram Reels, and YouTube Shorts. Start from that preset, or lock 9:16 and solve a different width.
What aspect ratio should an Instagram portrait use?
A common Instagram feed portrait is 4:5, often exported at 1080×1350. Square posts are 1:1, often 1080×1080. Stories and Reels use 9:16, often 1080×1920. Landscape feed images are often near 1.91:1; enter the pixels you were given and KeepRatio will simplify them.
How do I use the CSS aspect-ratio property?
Copy the declaration from the result, for example aspect-ratio: 16 / 9;. Put it on a container so the box keeps that proportion as the layout reflows. The two numbers match the simplified W:H ratio.
Can I lock a ratio and calculate only one side?
Yes. Choose Lock ratio, enter a ratio such as 16:9 or 9:16, and type the width or the height you already know. KeepRatio fills the other side. A 16:9 frame that is 1280 pixels wide is 720 pixels tall.
Are 1280×720 and 3840×2160 the same ratio as 1920×1080?
Yes. 1280×720, 1920×1080, and 3840×2160 all simplify to 16:9. They differ in resolution, not in shape. 1080×1920 is the same pixel count as HD turned on its side, and it simplifies to 9:16.
Does KeepRatio upload images or batch crop?
No. This version does not upload files and does not crop a batch of images. You type the dimensions you already have. The math runs in your browser on keepratio.com.