Aspect Ratio Calculator

How to calculate an aspect ratio or matching size

1. Choose Find aspect ratio, or Calculate matching pixel size if you already know one target dimension.
2. Enter width and height in the same unit, or enter ratio parts such as 16 and 9. Decimal ratio parts are accepted too.
3. For a matching size, choose target width or target height and enter that side in whole pixels. The other side is calculated for you.
4. Read the exact ratio or new pixel dimensions. Check any rounding notice, open the calculation details if useful, and copy the result.

What this aspect ratio calculator does

• Reduces width and height to an exact whole-number ratio, keeping width first.
• Accepts existing dimensions and decimal ratio parts without guessing a nearby standard.
• Calculates one missing pixel dimension from a chosen width or height.
• Clearly marks a derived dimension rounded to the nearest pixel and shows the resulting ratio in the details.
• Keeps calculations in page memory and provides a localized result to copy, without a file upload.

When a ratio or matching size helps

• Check whether a photo, video frame or presentation shape has the proportions you expected before editing or exporting it elsewhere.
• Plan the height for an image at a chosen website width, or the width for a fixed-height layout.
• Find the exact ratio of a nonstandard resolution instead of relying on a rounded screen or format label.

Understanding width, height and proportional sizes

An aspect ratio compares width with height, in that order. A 16:9 rectangle is wider than it is tall; 9:16 is portrait and 1:1 is square. A ratio describes shape, not the number of pixels or the physical size.

The exact ratio comes from dividing both entered values by their greatest common divisor after accounting for decimal places. Thus 1920 × 1080 becomes 16:9, while 1920 × 1200 reduces to 8:5, the same proportion often written 16:10.

To calculate a matching height, multiply the target width by the original height and divide by the original width. To calculate a matching width, multiply the target height by the original width and divide by the original height.

Useful starting ratios include 16:9, 9:16, 1:1, 4:3, 3:2 and 4:5. Enter their two parts as width and height. A decimal ratio such as 1.85:1 is entered as 1.85 and 1; it reduces exactly to 37:20.

Raster dimensions must be whole pixels. When the calculated side is fractional, this tool rounds it to the nearest pixel, with half-pixel ties upward. The ratio can change, noticeably for tiny sizes. The target side is not rounded or altered.

Use a decimal point or comma for source values and do not group digits: 1,000 means one, while 1000 means one thousand. For physical print dimensions, PPI and fit or crop checks, use the separate Print Size tool.

Worked aspect ratio and pixel-size examples

1920 wide and 1080 high reduce exactly to 16:9. A target width of 1280 pixels gives a height of 720 pixels with no rounding.

For a 9:16 portrait ratio, a target width of 1080 pixels gives 1080 × 1920 pixels.

1366 × 768 reduces to 683:384, not exactly 16:9. Likewise, 3440 × 1440 reduces to 43:18, not exactly 21:9.

At 16:9 and a target width of 1000 pixels, the exact height is 562.5. The result is about 1000 × 563 pixels; that whole-pixel size is not exactly 16:9.

At 2:1 and a target width of one pixel, the exact height is half a pixel. Rounding gives about 1 × 1 pixel, now square. Very small targets can change the shape substantially.

What the dimensions do not guarantee

This tool calculates numbers; it does not resize, crop, pad, compress or improve an image or video file.

Width and height must use the same unit. Pixel-based shape assumes square pixels; anamorphic display corrections and physical-size or PPI conversions are not included.

Source values accept 0.001–1,000,000 with up to three decimal places. Target and rounded output dimensions accept 1–1,000,000 whole pixels. These are calculator limits, not platform or file-format limits.

A matching size does not confirm upload acceptance, codec requirements, image quality or suitability for a device. Check those requirements separately; rounding may change the exact ratio.

Your dimension inputs

The tool keeps figures in page memory, with no upload, saved history, account or share link containing them. Copy happens only when requested.

The surrounding website can make normal requests under its existing consent and analytics settings. Local calculation is not whole-site privacy certification.