Aspect Ratio Calculator
Enter any two dimensions to get the simplified aspect ratio, or choose a mode to solve for a missing width or height. The calculator handles every standard ratio from 1:1 square to 21:9 ultrawide, identifies the nearest named format, and shows the step-by-step working so you always understand the result.
What is an aspect ratio?
An aspect ratio is the proportional relationship between the width and height of a rectangular image, screen, or frame. It is expressed as two integers separated by a colon, such as 16:9 or 4:3. The numbers do not represent actual pixel counts; they represent the ratio in its simplest form. A 1920x1080 pixel frame and a 1280x720 pixel frame both have a 16:9 aspect ratio because both reduce to the same lowest terms. Aspect ratio matters whenever you are displaying, printing, cropping, or encoding media: keeping the original ratio prevents the stretching or squashing that occurs when width and height are scaled independently.
How the calculator works
Use "Find ratio from dimensions" to enter any two pixel (or unit) values and get the simplified ratio, the decimal equivalent, and the nearest named standard within 2%. Use "Find width from ratio + height" or "Find height from ratio + width" when you know the ratio and one side and need the other, for example when preparing a banner or thumbnail to an exact pixel spec. Use "Resize to new width" to proportionally scale an existing image: enter the original dimensions and your new width, and the calculator returns the correct new height and the percentage change. In every mode the "Show your work" panel shows the arithmetic so you can reproduce it in any image editor or script.
Aspect ratio in video and streaming
Modern broadcast and streaming uses 16:9 (1.78:1) as its base container. YouTube, Netflix, and most smart TVs default to this shape. Vertical mobile content uses the inverse 9:16. Cinematic releases often use wider ratios: 1.85:1 for the "flat" theatrical frame and 2.39:1 for anamorphic widescreen. When a 2.39:1 film is shown in a 16:9 container, the black bars above and below (letterboxing) fill the difference. Conversely, a 9:16 clip placed in a 16:9 frame gets black bars left and right (pillarboxing). Knowing your target ratio before you shoot or export saves time and avoids cropping surprises.
Aspect ratio in photography and print
Most digital cameras shoot in 3:2, matching the 35 mm film frame that photography standardised on decades ago. Social platforms then display images in their own containers: 1:1 for Instagram grid posts, 4:5 for portrait posts, and 1.91:1 for landscape posts. When you upload a 3:2 photo to a 1:1 container, the platform will crop or letterbox it unless you add white or blurred padding. For print, common paper ratios vary: A4/A3 sheets are close to 1:1.41 (the ISO 216 root-2 ratio), while 4x6 inch prints are exactly 3:2. Understanding these mismatches upfront lets you compose with the crop in mind rather than fixing it after the fact.
Common aspect ratios
| Ratio | Decimal | Common use |
|---|---|---|
| 1:1 | 1.000 | Square - Instagram grid, avatars, album art |
| 4:3 | 1.333 | Classic TV, old monitors, iPad video |
| 3:2 | 1.500 | DSLR photography, 35 mm film, tablets |
| 5:4 | 1.250 | Vintage monitors (1280x1024) |
| 16:9 | 1.778 | HD/4K TV, YouTube, Zoom, presentations |
| 16:10 | 1.600 | Widescreen laptops, MacBook displays |
| 21:9 | 2.333 | Ultrawide monitors, cinematic video |
| 32:9 | 3.556 | Super ultrawide gaming monitors |
| 9:16 | 0.563 | Vertical video - Reels, TikTok, Stories |
| 2:1 | 2.000 | Univisium, some smartphone UIs |
| 2.39:1 | 2.390 | Anamorphic widescreen (Cinemascope) |
Standard formats used in video production, photography, web design, and display hardware.
Frequently asked questions
What is the difference between 16:9 and 4:3?
16:9 is a wider, rectangular format with a decimal ratio of about 1.78. It became the global standard for HD television, YouTube, and most modern monitors. 4:3 has a decimal ratio of 1.33 and was the standard for CRT televisions and early computer monitors. If you play 16:9 content on a 4:3 screen without cropping, you get horizontal black bars (letterboxing). The two ratios share no common simple factor, so there is no clean zoom level that fills both without some cropping or padding.
How do I calculate an aspect ratio from pixel dimensions?
Divide both the width and height by their greatest common divisor (GCD). For 1920x1080, the GCD is 120, giving 16:9. For 2560x1440, the GCD is 80, also giving 16:9. The GCD is found using the Euclidean algorithm: repeatedly replace the larger number with the remainder of dividing the larger by the smaller until the remainder is zero. This calculator does that automatically and shows the step-by-step working.
How do I find the height for a given width and ratio?
Use the formula: height = width x (ratio height / ratio width). For a 16:9 frame at 1920 px wide: height = 1920 x (9 / 16) = 1080 px. You can do the reverse for width: width = height x (ratio width / ratio height). Switch the calculator to "Find width" or "Find height" mode and it applies the formula automatically.
What does a 2.39:1 aspect ratio mean?
2.39:1 (sometimes written 2.40:1) is the anamorphic widescreen format used in many theatrical films. It is noticeably wider than standard HD video (1.78:1), which is why films shot in this format have the prominent black bars when shown on a 16:9 screen. The format is associated with a cinematic look and is popular in music videos and high-budget productions that want a widescreen aesthetic.
Why does resizing an image distort it?
Distortion happens when width and height are not scaled by the same factor. If you resize a 1920x1080 image to 1280x900 instead of 1280x720, the horizontal scale factor is 1280/1920 = 0.667 while the vertical is 900/1080 = 0.833: those differ, so subjects are squeezed horizontally. Always lock the aspect ratio when resizing in an image editor, or use this calculator to confirm the correct target dimensions before you apply the resize.
What aspect ratio should I use for social media?
It depends on the platform and placement. Instagram feed posts are displayed at 1:1 (square) or 4:5 (portrait), Facebook and LinkedIn at 16:9 (landscape), YouTube thumbnails and video at 16:9, TikTok and Instagram Reels at 9:16 (vertical), and Twitter/X cards at 2:1 or 16:9. Creating your master file at the native ratio of each destination avoids auto-cropping and keeps subjects centred.