Screen Size Calculator
Calculate screen diagonal size from width and height.
Diagonal
137.9cm
- Diagonal
- 54.3 inches
v1.0 · Reviewed September 2026
How this is worked out
The diagonal is found with Pythagoras from the width and height, then converted to inches at 2.54 cm per inch.
Worked example
- 120 cm wide
- 68 cm high
√(120² + 68²) = 137.9 cm, ÷ 2.54
A diagonal of 137.9 cm, or 54.3 inches
Assumptions and limits
- Measure the visible screen area only. Including the bezel or stand overstates the size.
- Advertised screen sizes are usually rounded, so a set sold as 55 inch may measure a little under.
- Says nothing about resolution or picture quality.