Aspect Ratio Calculator

How it works

Worked examples

1. 1

   Find height for a 16:9 frame that is 1920 pixels wide

   1. Multiply 1920 by 9.
   2. Divide the result by 16.
   3. The matching height is 1080.

   1920 × 1080 preserves a 16:9 aspect ratio.

   Try these numbers
2. 2

   Find width for a 4:3 frame that is 900 pixels high

   1. Multiply 900 by 4.
   2. Divide the result by 3.
   3. The matching width is 1200.

   1200 × 900 preserves a 4:3 aspect ratio.

   Try these numbers
3. 3

   Simplify 3840 × 2160

   1. Find the greatest common divisor of 3840 and 2160: 240.
   2. Divide both dimensions by 240.
   3. The reduced components are 16 and 9.

   3840 × 2160 simplifies to 16:9.

   Try these numbers

Inputs and results

Width

The known or existing horizontal dimension. Use positive values only.

Height

The known or existing vertical dimension. Use positive values only.

Ratio width

The horizontal component of the target ratio, such as 16 in 16:9.

Ratio height

The vertical component of the target ratio, such as 9 in 16:9.

Missing dimension

The width or height required to preserve the selected aspect ratio.

Simplified ratio

Integer width and height reduced by their greatest common divisor.

When to use it

• Calculate a missing width or height before resizing a frame, image, slide, canvas, or layout box while preserving a chosen proportion.
• Simplify positive integer pixel dimensions such as 3840 × 2160 to their reduced ratio components.
• Check the proportional dimension required when one side and the target ratio are already known.

Common mistakes

• Using width and height in different measurement units, which makes the resulting proportion meaningless.
• Treating a ratio such as 16:9 as if it required dimensions of exactly 16 by 9 instead of any proportional multiple.
• Rounding an intermediate missing dimension too early and then assuming the rounded pair still preserves the original ratio exactly.

What it does not do

• The calculator preserves mathematical proportion only; it does not crop, stretch, letterbox, or choose a framing strategy for visual content.
• It does not apply platform-specific upload limits, codec alignment rules, even-number requirements, safe areas, or responsive breakpoint decisions.
• Ratio simplification is exact for positive integer dimensions; it is not a best-fit approximation tool for arbitrary decimal measurements.

Method and assumptions

Assumptions

• Width and height are expressed in the same unit, or both are unitless pixel counts.
• Ratio components are greater than zero.
• Display rounding, codec-specific even-number requirements, crop recommendations, and platform upload rules are separate concerns and are not silently applied.

Edge cases

• A zero or negative dimension is invalid because an aspect ratio requires positive dimensions.
• Fractional dimensions can be used for proportional solving, but integer-only simplification requires positive integers.
• Changing only one dimension without preserving the ratio changes the shape of the frame.

Sources and corrections

This calculator uses an elementary formula, so it needs no outside data source. The method, the rounding rules and how a reported error is corrected are set out in the site standards.

• Calculation Methodology
• Sources Policy
• Corrections Policy