TV Size Calculator
Convert TV diagonal size to width and height in inches and cm. Supports 16:9 and 4:3 aspect ratios.
How to use this tool
- Enter diagonal size and aspect ratio in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your width and the full breakdown beneath it.
Enter your TV's diagonal measurement to find the actual width and height of the screen.
Formula
For 16:9 aspect ratio:
Width (in) = Diagonal × 16 / √(16² + 9²) = Diagonal × 16 / 18.358
Height (in) = Diagonal × 9 / 18.358
For 4:3 aspect ratio:
Width (in) = Diagonal × 4 / 5 Height (in) = Diagonal × 3 / 5
cm = inches × 2.54
How it works
TV diagonal measurements follow the Pythagorean theorem: for a rectangle with width-to-height ratio w:h, the diagonal d satisfies d² = w² + h², so width = d × w / √(w² + h²) and height = d × h / √(w² + h²). Centimetre values are obtained by multiplying each inch dimension by 2.54. A very common mistake is assuming that a 55-inch TV has a 55-inch wide screen — the 55 inches refers to the diagonal of the display panel only, not the width; the actual width of a 16:9 panel is about 48 inches, and the surrounding bezel adds additional width to the overall set.
Worked example
Finding width and height of a 55-inch 16:9 TV
- Diagonal = 55 in, aspect ratio = 16:9.
- Calculate denominator: √(16² + 9²) = √(256 + 81) = √337 ≈ 18.358.
- Width = 55 × 16 / 18.358 ≈ 47.94 in; Height = 55 × 9 / 18.358 ≈ 26.96 in.
- Convert to cm: 47.94 × 2.54 ≈ 121.76 cm; 26.96 × 2.54 ≈ 68.49 cm.
Width: 47.94 in (121.76 cm) | Height: 26.96 in (68.49 cm)
Common mistakes to avoid
- Using the diagonal measurement to estimate how wide the TV will be without calculating -- a 65-inch TV at 16:9 ratio is about 56.7 inches wide, not 65 inches; it may not fit the intended shelf or wall space.
- Forgetting to include the TV bezel in space planning -- the calculator outputs screen dimensions; the total unit width (including frame) is typically 1-2 inches wider than the screen.
- Comparing TVs by diagonal alone without checking resolution -- a 75-inch 1080p TV has lower pixel density than a 55-inch 4K TV; at typical viewing distances the larger 1080p set may look less sharp.
Key terms
- Diagonal size
- The measurement of a TV screen from one corner to the opposite corner; it is the figure used in marketing and does not equal the width of the screen.
- Aspect ratio
- The proportional relationship between a screen's width and height; 16:9 is the widescreen standard for HDTV and most modern content, while 4:3 was the standard for older CRT televisions.
- 16:9
- The standard widescreen aspect ratio for HDTV, Blu-ray, and most streaming video; produces screens that are approximately 1.78 times wider than they are tall.
- Pythagorean theorem
- The geometric principle (a² + b² = c²) used to relate the width, height, and diagonal of a rectangular screen, enabling any one dimension to be calculated from the other two.
Frequently asked questions
- How wide is a 55-inch TV?
- A 55-inch 16:9 TV is approximately 47.9 inches (121.8 cm) wide and 27.0 inches (68.5 cm) tall.