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Aspect Ratio Calculator

Calculate a missing width or height from a known aspect ratio, or find the ratio between two dimensions.

Guide

Interactive workspace

No account required
Aspect Ratio Calculator
Common aspect ratio presets
Platform presets (fill ratio and size)
Calculated height
1080px
Decimal ratio
1.7778:1
Orientation
Landscape
Total pixels
2,073,600
Megapixels
2.07 MP
Preview (true proportions)
1920 × 1080

Use this size in code

aspect-ratio: 16 / 9;
.ratio-box::before { content: ""; display: block; padding-bottom: 56.25%; }
<img src="image.jpg" width="1920" height="1080" alt="" />

The width and height attributes on the img tag let the browser reserve the right space before the image loads, which prevents layout shift (CLS).

How to use it

  1. Enter dimensions to inspect a ratio or choose a target ratio.
  2. Use the supported known-dimension controls to calculate the matching size.
  3. Review rounding before applying the dimensions in an image editor.
What is Aspect Ratio Calculator?

Calculate a missing width or height from a known aspect ratio, or find the ratio between two dimensions.

How it works

SiteIndex scales a known width or height using your target ratio to calculate the missing dimension, and can also reduce two dimensions to their simplest whole-number ratio.

Common aspect ratios and where they are used

Aspect ratio describes the proportional relationship between width and height. Keep the same ratio when you resize an image or video to avoid stretching.

  • 16:9

    Widescreen video and modern displays

  • 4:3

    Older monitors, presentations and classic video

  • 1:1

    Square social posts and profile images

  • 9:16

    Vertical short-form video and stories

  • 21:9

    Ultrawide monitors and cinematic video

  • 3:2

    Many camera photographs

  • 16:10

    Laptop and productivity displays

Use the Golden Ratio Calculator to explore proportional layouts, or use the Image Resizer to resize an actual image file.

Common uses
  • Find the correct height for a banner at a fixed width and ratio.
  • Check whether an image matches a common ratio like 16:9 or 4:3.
  • Resize a design proportionally without distorting it.
Limitations
  • Dimension calculation alone does not crop, resample, or change an image file. Pixel rounding can slightly change the represented ratio.
Frequently asked questions
Does this crop or resize my actual image?
No. This only calculates dimensions; use the Image Resizer tool to resize an actual image file.

Related tools

Image Resizer
Resize JPG, PNG, and WebP images locally with aspect-ratio locking, presets, and export-quality controls.
PX / REM Calculator
Convert px to rem and rem to px with a configurable base font size, or switch to px to em for sizing relative to a parent font.
Golden Ratio Calculator
Calculate the complementary dimension of a layout using the golden ratio, approximately 1.618.
Image Cropper
Crop, rotate, and flip an image locally with percentage-based bounds. Your image is processed in the browser, never uploaded.
Border Radius Generator
Adjust each corner radius independently and copy the resulting CSS border-radius declaration.