Screen Size Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/10/2026
A screen's diagonal in inches converts to centimeters with the exact factor 2.54. A 24-inch screen therefore measures 60.96 cm diagonally, that is about 53.1 cm wide and 29.9 cm tall at a 16:9 aspect ratio.
Explanation
A screen's commercial size (TV, monitor, smartphone) almost always refers to its diagonal, expressed in inches by historical industry habit even outside English-speaking countries. Since the inch has been defined at exactly 2.54 cm since 1959 (see our length conversion calculator for the other imperial units), the conversion to centimeters is immediate. Knowing only the diagonal, however, is not enough to picture the screen's real size: you also need its aspect ratio (the width-to-height ratio, such as 16:9 for most current TVs and monitors, or 4:3 for older screens). Applying the Pythagorean theorem to a rectangle of known diagonal and given width-to-height ratio recovers the exact width and height: two 24-inch screens with different aspect ratios (16:9 versus 4:3, for example) have neither the same width nor the same height, despite an identical diagonal.
Example: a 24-inch screen at 16:9 aspect ratio
Inputs
Diagonal: 24 inches. Aspect ratio: 16:9.
Calculation
Diagonal = 24 × 2.54 = 60.96 cm. Height = 60.96 ÷ √((16/9)² + 1) ≈ 29.89 cm. Width = 29.89 × (16/9) ≈ 53.13 cm.
Result
This screen measures about 61 cm diagonally, at 53.1 cm wide and 29.9 cm tall.
Frequently asked questions
Why don't two screens with the same diagonal have the same visible area?
Because the diagonal alone does not fix the shape of the rectangle: a 21:9 (ultra-wide) screen and a 16:9 screen with the same diagonal have different widths and heights, the ultra-wide screen being more stretched horizontally and therefore slightly shorter. Comparing two screens therefore requires knowing both the diagonal and the aspect ratio, not just the diagonal advertised in the store.
Is 16:9 really the most common aspect ratio?
Yes, it is the standard aspect ratio of nearly all TVs and the majority of computer monitors sold today, inherited from high-definition television. The 16:10 ratio, slightly squarer, is still used on some office- and productivity-oriented monitors, while 21:9 targets immersive uses (gaming, multi-window video editing) and 4:3 is now found only on older equipment.
Does this visible size correspond exactly to what the manufacturer advertises?
Almost: this calculation gives the diagonal and dimensions of the theoretical active display area. Some manufacturers advertise a slightly rounded diagonal, and the actually visible area can be marginally reduced by the screen bezel depending on the model, a difference generally less than a few millimeters. To estimate image sharpness rather than physical size, see our image resolution calculator.