Pixel Aspect Ratio Calculator
Enter a pixel width and height to see the simplified aspect ratio, or pick a standard ratio and one dimension to find the other. The calculator works in both directions: pixels to ratio and ratio to pixels. It also shows total pixel count, megapixels, and orientation. Use the preset menu for instant access to 16:9, 4:3, 1:1, 3:2, 21:9, and other common formats.
What is aspect ratio?
Aspect ratio is the proportional relationship between a frame's width and its height, expressed as two integers separated by a colon, such as 16:9 or 4:3. It describes the shape of the frame without saying anything about its size: a 1280x720 image and a 3840x2160 image share the same 16:9 ratio even though one is nine times larger in pixel count. When you resize an image while keeping its aspect ratio constant, you are scaling both dimensions by the same factor, so the picture looks the same shape at any resolution. Aspect ratio matters in video production, photography, web design, and UI development. If you crop or stretch a frame to a different ratio without correcting it, horizontal lines warp into diagonal ones and circles turn into ovals. Most professional tools let you lock the ratio during resizing, but you sometimes need to calculate the missing dimension manually, which is exactly what this calculator does.
How to calculate aspect ratio from pixel dimensions
To find the aspect ratio of a frame, divide both the width and the height by their greatest common divisor (GCD). The GCD is the largest integer that divides both numbers evenly. For example, a 1920x1080 image: GCD(1920, 1080) = 120, so 1920/120 = 16 and 1080/120 = 9, giving 16:9. The decimal form of the ratio is simply width divided by height. For 1920x1080 that is 1920/1080 = 1.7778. Values above 1 mean the frame is wider than it is tall (landscape), values below 1 mean it is taller than it is wide (portrait), and a value of exactly 1 means square. To find a missing dimension when the ratio is known, rearrange the proportion: height = width x ratio_H / ratio_W, and width = height x ratio_W / ratio_H. A 1080p height on a 16:9 frame gives width = 1080 x 16 / 9 = 1920 px.
Pixel aspect ratio vs. display aspect ratio
Display aspect ratio (DAR) is the ratio of width to height as you see it on screen. Pixel aspect ratio (PAR) is the shape of each individual pixel itself. Most modern digital formats and displays use square pixels (PAR 1:1), meaning each pixel is as wide as it is tall, so the DAR and the pixel grid match exactly. Non-square pixels historically appeared in standard-definition digital video, particularly in the DV and MPEG-2 formats used before HD. A 720x480 NTSC DV frame with PAR 10:11 was stored in a non-square pixel grid but displayed at a 4:3 or 16:9 DAR depending on the encoder setting. Mixing up PAR and DAR in a video editor caused the classic "squashed face" artifact. When working with modern HD (720p, 1080p) or UHD (4K) footage, PAR is always 1:1, so the only ratio that matters is the display aspect ratio, which is what this calculator computes.
Common aspect ratios and when to use each one
16:9 (decimal 1.778) is the universal standard for widescreen content, used by YouTube, Netflix, modern TV broadcasts, and the vast majority of computer monitors and laptops. Almost all video production targets 16:9 unless there is a specific reason to do otherwise. 4:3 (decimal 1.333) was the standard for analogue TV, classic computer monitors, and early digital cameras. It remains common for slide presentations (PowerPoint default is 4:3 or 16:9) and tablet screens. 1:1 (square) is the signature Instagram grid ratio and is also used for album art and some social media profile images. It requires no cropping for either landscape or portrait source images if you are willing to pad with a background. 3:2 (decimal 1.5) matches the sensor shape of full-frame and APS-C digital SLR cameras. Prints at 6x4 inches and 12x8 inches are 3:2. 9:16 (decimal 0.5625) is 16:9 rotated, used for vertical video on TikTok, Instagram Reels, and YouTube Shorts. 21:9 (decimal 2.333) is used for ultrawide monitors and cinematic widescreen. Many streaming services add thin black bars on 21:9 content to fill 16:9 TVs.
Common display resolutions and their aspect ratios
| Name | Width (px) | Height (px) | Aspect ratio | Megapixels |
|---|---|---|---|---|
| SD 480p | 640 | 480 | 4:3 | 0.31 MP |
| SD 576p | 720 | 576 | 5:4 | 0.41 MP |
| HD 720p | 1280 | 720 | 16:9 | 0.92 MP |
| Full HD 1080p | 1920 | 1080 | 16:9 | 2.07 MP |
| 2K QHD | 2560 | 1440 | 16:9 | 3.69 MP |
| 4K UHD | 3840 | 2160 | 16:9 | 8.29 MP |
| 8K UHD | 7680 | 4320 | 16:9 | 33.18 MP |
| Cinema DCI 2K | 2048 | 1080 | ~17:9 | 2.21 MP |
| Cinema DCI 4K | 4096 | 2160 | ~17:9 | 8.85 MP |
| Square 1:1 | 1080 | 1080 | 1:1 | 1.17 MP |
| Classic DSLR 3:2 | 3000 | 2000 | 3:2 | 6.00 MP |
| Ultrawide 21:9 | 2560 | 1080 | 21:9 | 2.76 MP |
Standard resolutions used in video, photography, and screen design. All resolutions listed assume square pixels (PAR 1:1).
Frequently asked questions
How do I find the aspect ratio of an image?
Divide both the pixel width and the pixel height by their greatest common divisor. For a 1280x800 image, GCD(1280, 800) = 160, so the ratio is 8:5. You can also express it as a decimal by dividing width by height: 1280 / 800 = 1.6. This calculator does both steps for you automatically in the "Pixels to ratio" mode.
What is the most common aspect ratio for video?
16:9 is by far the most common ratio for video content today. It is used by YouTube, Netflix, modern broadcast TV, Blu-ray, and most computer monitors and laptops. If you are producing video without a specific platform requirement, 16:9 at 1080p (1920x1080) or 4K (3840x2160) is the safe default.
What resolution gives a 16:9 ratio?
Any resolution where width / height = 1.7778 (16 divided by 9) is 16:9. Common examples are 1280x720 (HD), 1920x1080 (Full HD), 2560x1440 (QHD), and 3840x2160 (4K UHD). You can find the height for any 16:9 width by multiplying the width by 9 and dividing by 16.
What is pixel aspect ratio (PAR) and how is it different from display aspect ratio?
Display aspect ratio (DAR) is the visible shape of the whole frame, for example 16:9. Pixel aspect ratio (PAR) is the shape of each individual pixel. Modern digital video and all current displays use square pixels (PAR 1:1), so the two terms mean the same thing in practice. Non-square pixels existed in older SD video formats (NTSC DV, PAL DV) and some legacy codecs. If you see a "squashed" picture in an old video editor, mismatched PAR is often the cause.
How do I resize an image to a specific aspect ratio without distortion?
To change the aspect ratio without distortion, you must either crop the image (cut pixels from one edge) or letterbox/pillarbox it (add padding bars). If you want to resize to the same ratio at a different resolution, simply pick the new width and multiply by ratio_H / ratio_W to get the height, or use the "Ratio to height" mode in this calculator. Changing the canvas dimensions without cropping or padding stretches the image and causes distortion.
What is the difference between 4K and 4K DCI?
4K UHD (the consumer standard) is 3840x2160, a 16:9 ratio. 4K DCI (the cinema standard defined by the Digital Cinema Initiatives) is 4096x2160, which is very close to 17:9. The DCI frame is wider to accommodate native 1.90:1 or 2.39:1 scope cinema content. When you export from a cinema camera in DCI 4K and deliver for TV or streaming, the sides are cropped or the footage is letterboxed to fit the 16:9 UHD container.