Checked Math

Media math

Aspect Ratio Calculator

Use width and height to simplify an existing aspect ratio, or enter a target ratio and one known dimension to calculate the other without stretching the proportions.

Calculation class
Exact — determined entirely by the arithmetic identity, with no estimation layer.
Formula version
aspect.dimension@1.0.0

Calculator

Aspect ratio calculator

Enter your current dimensions and the ratio you want to fit. Width and height must use the same measurement unit; ratio values are unitless.

Choose what you want to find
Target ratio
Preset applied

Result

New height

1,080px

1,920 × 9 ÷ 16 = 1,080

At a width of 1,920 pixels and a ratio of 16 : 9, the height is 1,080 pixels.
Resized width
1,920px
Resized height
1,080px
Dimension comparison
16 : 9
1,920 px1,080 px1,920 px1,080 px

As entered: 1,920 × 1,080 px

Both frames are drawn from the same corner at one shared scale, so their relative sizes are exact. The calculator resizes proportionally — it does not crop.

Formula

Identity

height = width × ratioHeight ÷ ratioWidth

With your values

1920 × 9 ÷ 16

The reverse form is width = height × ratioWidth / ratioHeight. Existing positive integer dimensions can also be reduced with their greatest common divisor.

Calculation steps

  1. Formulaheight = width × ratioHeight ÷ ratioWidth
  2. Substitute values1920 × 9 ÷ 16
  3. Height1,080
On this page

How this calculation works

An aspect ratio describes the proportional relationship between width and height. A 1920 × 1080 frame simplifies to 16:9 because both dimensions can be divided by the same greatest common divisor.

When one dimension is missing, the same proportion can be preserved by multiplying the known dimension by the opposite ratio component and dividing by its matching ratio component.

Inputs and outputs

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.

Worked examples

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.

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.

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.

When this calculator is useful

  • 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.

What this calculator 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.

Common mistakes to avoid

  • 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.

Methodology and assumptions

Missing dimensions are calculated directly from the proportional identity; no external dataset or changing factual input is used.

Ratio simplification is restricted to positive integer dimensions so the result is deterministic and exact.

  • 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.