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Aspect Ratio Calculator Online
Free aspect ratio calculator. Enter width and height to get the simplified ratio and a preview box.
Aspect ratios without guessing
An aspect ratio describes the relationship between width and height, not an actual size. That is why 16:9 works for a 1280x720 video and a 3840x2160 one: scale both numbers by the same factor and the shape is unchanged. Once you have the ratio, any single known dimension gives you the other.
The everyday use is resizing without distortion. A 1920x1080 image scaled to a width of 800 needs a height of 450, and the ratio tells you that before you open an editor. It works backwards too: if a layout reserves a height of 400 for a 16:9 slot, the matching width is about 711.
The trap is assuming two nearby ratios are the same. 1920x1080 is 16:9 but 1920x1200 is 16:10, and the difference shows up as letterboxing the moment a video is placed in a container built for the other. When a design mixes ratios, note them beside each size instead of trusting memory.
FAQ
- How is 16:9 computed?
- Width and height are reduced by their greatest common divisor.
- Useful for social images?
- Yes — presets cover common sizes quickly.
- Uploaded?
- No.
- How do I work out an aspect ratio?
- Divide both dimensions by their greatest common divisor. 1920 and 1080 both divide by 120, leaving 16:9. For sizes that do not reduce to a familiar ratio, compare the two numbers as a decimal instead: 1.78 is 16:9 and 1.33 is 4:3, which is enough to tell them apart.
- What is the difference between 16:9 and 4:3?
- 16:9 is the modern widescreen shape at about 1.78 to 1, and 4:3 is the older television shape at 1.33 to 1. Putting 4:3 footage in a 16:9 frame adds side pillars, and putting 16:9 in a 4:3 frame adds bars top and bottom. Neither is wrong; the mismatch is what looks broken.
- Which aspect ratio should social video use?
- Vertical 9:16 for short-form feeds, square 1:1 for general posts, and 16:9 for embedded or landscape players. Reusing a landscape cut in a vertical feed shrinks it to a small band, so the ratio choice usually matters more than the resolution.