Free · Measurement and planning

CSS Box Width Height and Ratio

Relate a CSS box’s width and height through selected ratio presets. The 4:3 preset has an independently reviewed arithmetic correction.

  • Formula & worked example
  • Private in your browser
  • No signup
Go to tool

Calculator inputs

Loading calculator…

How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A width of 12 at a 4:3 ratio gives height 9.

Width / height = aspect ratio.

Worked example

Enter these known values and leave the other values blank.

Box width-to-height ratio
SVGA / XGA (4:3)
Box width
12
Box height
9

Assumptions and limitations

  • Use positive width and height in matching units.
  • Ratio means width divided by height. It describes rectangle shape and does not change image resolution.
  • Results follow the stated ideal arithmetic model. Display rounding does not change the underlying calculation.
  • Supply sufficient known values and leave the desired quantity blank. Controls retain captured inverse branches and units.
  • Some retained ratio presets use rounded decimal constants, including 4:3. Exact integer-ratio geometry can differ slightly from these approximations.
  • The reviewed 4:3 selector uses decimal 4/3 with 100 places; the captured 10/3-like value is corrected. Use the same length unit for width and height.
  • If a retained lock prevents a reverse calculation, unlock the quantity you want to solve before supplying the known values.

Common questions

What does the worked example demonstrate?

Width / height = aspect ratio.

Can I change the measurement units?

Available selectors convert the entered physical quantity. Use compatible units for all related quantities.

Why can a result be blank?

A missing input, invalid denominator or underdetermined relationship cannot provide a unique finite result.

References

The captured 4:3 preset has value 3.33333333333, which is incorrect. Replace only that preset with a high-precision decimal 4/3; all other presets remain captured approximations.

Explore measurement and planning or browse all everyday life calculators.