Enter your original width and height, then provide either a new width or new height — the Aspect Ratio Calculator solves for the missing dimension while preserving your exact ratio. You also get the simplified aspect ratio (e.g. 16:9) and the nearest standard display ratio for quick reference.
Aspect Ratio
--
Calculated New Dimension
--
Ratio as Decimal
--
Nearest Standard Ratio
--
Original Megapixels
--
An aspect ratio is the proportional relationship between the width and height of an image, screen, or video frame. It is expressed as two numbers separated by a colon, such as 16:9 or 4:3. The ratio describes shape, not actual size — a 1920×1080 screen and a 1280×720 screen both share a 16:9 aspect ratio.
Divide both the width and height by their greatest common divisor (GCD). For example, 1920 and 1080 share a GCD of 120, so 1920÷120 = 16 and 1080÷120 = 9, giving a 16:9 ratio. You can also express it as a decimal by simply dividing width by height (1920÷1080 ≈ 1.7778).
Use the formula: (Original Height ÷ Original Width) × New Width = New Height. For example, if your image is 1600×1200 and you want a new width of 400, calculate (1200 ÷ 1600) × 400 = 300. The result maintains your original proportions perfectly.
Aspect ratios are used in photography, video production, web design, advertising, and display manufacturing to ensure images and videos scale correctly without distortion. Knowing the ratio lets you resize content for different platforms — such as cropping a landscape photo for a square Instagram post — without stretching or squashing it.
The most widely used ratios are 16:9 (widescreen HD TV and YouTube), 4:3 (older monitors and TVs), 1:1 (square, popular on Instagram), 9:16 (vertical mobile video and Stories), 3:2 (DSLR cameras and 35mm film), and 21:9 (ultra-wide monitors and cinematic displays). 2.35:1 is common in theatrical film.
'Fit' (also called letterboxing or pillarboxing) scales your content so it fits entirely within the new frame, adding black bars on the sides or top/bottom. 'Fill' (also called cropping or zooming) scales content so it covers the entire frame, but parts of the image may be cropped out. The right choice depends on whether preserving all content or filling the frame matters more.
Aspect ratio itself does not directly affect file size — resolution (the total pixel count) does. However, changing the aspect ratio by cropping reduces the number of pixels and can lower resolution. Always start with the highest resolution source possible before resizing or cropping to a new ratio.
It depends on the platform and placement. For YouTube and most video platforms, 16:9 is standard. Instagram feed posts work best at 1:1 (square) or 4:5 (portrait). Instagram and TikTok Stories use 9:16. Facebook and Twitter generally prefer 16:9 for shared videos. Always check the platform's current guidelines as they update frequently.