LifeTally
Screen width and height calculator
How wide and tall is my image area from its diagonal and aspect ratio?
Calculate a flat rectangular image area's dimensions in centimetres and inches from your own diagonal and width-to-height ratio.
Your diagonal and proportions
For 4:3, enter 4 and 3. Width follows the first part and height the second; the calculator does not rotate them. Fractions are allowed. A zero diagonal is the zero-size limiting case; both ratio parts must stay positive.
How the estimate works
For width:height = a:b, the diagonal of the matching rectangle is proportional to √(a² + b²). Multiply your diagonal by a or b and divide by that factor to get width or height in inches. One inch is exactly 2.54 cm. Area is calculated from the unrounded geometry.
W = D × a ÷ √(a² + b²)
H = D × b ÷ √(a² + b²)
cm = in × 2.54
A = D² × a × b ÷ (a² + b²) × 2.54²Models only a flat rectangular image area with the entered diagonal and proportions. It excludes the frame, stand, mounting clearances, curvature, rounded corners, cutouts and image cropping. It does not calculate pixel density or viewing distance. Check the actual external dimensions separately; this is not a guarantee that a device fits.
NIST: the exact inch-to-metric conversion ↗OpenStax: Pythagorean theorem and rectangle area ↗
Check the filled example
Chosen example: a 10-inch diagonal with a 4:3 width-to-height ratio gives 8 × 6 inches, or 20.32 × 15.24 cm. The rectangular area is 309.6768 cm² and the diagonal is 25.4 cm. These are illustrative inputs, not a recommended screen size or aspect ratio.
Accepted input values
- Image diagonal, inches
- 10
- Width part of the ratio (a)
- 4
- Height part of the ratio (b)
- 3