About the TV Size Calculator
TV and monitor sizes are sold by their diagonal measurement, which says little about whether the screen will fit your wall, cabinet or alcove. This TV size calculator converts the advertised diagonal into the actual width and height of the picture area, in inches and centimetres, for the common aspect ratios: 16:9 for TVs, 21:9 for ultrawide monitors, 16:10 for laptops and 4:3 for older sets.
It is handy when you are shopping for a new TV, planning a wall mount or entertainment unit, or deciding whether upgrading from a 55-inch to a 65-inch set is worth it. Enter a second size to see how much more screen area you gain — because area grows with the square of the diagonal, a small step up in inches is a big jump in picture.
Results are for the visible screen only. The TV’s outer dimensions are slightly larger because of the bezel and stand, so check the manufacturer’s spec sheet for exact cabinet measurements.
With the default inputs, the screen width is 56.7 in. Change any value above to recalculate instantly.
How to use the tv size calculator
- 1Enter the advertised screen size (the diagonal) in inches.
- 2Choose the aspect ratio — 16:9 for almost all modern TVs.
- 3Optionally enter your current TV size to compare.
- 4Read the width, height and area in inches and centimetres.
- 5Add the bezel allowance before buying furniture or a wall mount.
Formula and method
A screen is a rectangle whose diagonal D forms the hypotenuse of a right triangle with the width and height. For an aspect ratio a:b, the Pythagorean theorem gives the diagonal of an a × b rectangle as √(a² + b²), so width and height scale by D ÷ √(a² + b²).
For 16:9, √(16² + 9²) ≈ 18.36, so width ≈ 0.872 × D and height ≈ 0.490 × D. Area is width × height, and centimetres are inches × 2.54. Comparing sizes by area shows the true difference in picture size.
- D
- Diagonal screen size (inches)
- a
- Aspect ratio width component (e.g. 16)
- b
- Aspect ratio height component (e.g. 9)
Worked examples
65-inch 16:9 TV vs a 55-inch
A 65" 16:9 screen is 65 × 16 ÷ 18.36 ≈ 56.7" wide and 65 × 9 ÷ 18.36 ≈ 31.9" tall, or about 144 × 81 cm. Its 1,805 sq in of picture is about 40% more than a 55" TV.
34-inch ultrawide monitor
For 21:9 the diagonal factor is √(21² + 9²) ≈ 22.85. A 34" ultrawide is therefore about 31.3" wide and 13.4" tall — roughly 79 × 34 cm of screen. Most “21:9” monitors are really 3440 × 1440 (about 2.39:1), so the real panel is a little wider and shorter, about 31.4" × 13.1".
Upgrading from 65 to 75 inches
A 75" TV measures about 65.4" × 36.8" with 2,404 sq in of picture. Although the diagonal is only 15% larger than 65", the picture area is about 33% larger because area grows with the square of the diagonal.
Frequently asked questions
What are the dimensions of a 65 inch TV?+
A 65-inch 16:9 TV has a screen about 56.7 inches wide and 31.9 inches tall (144 × 81 cm). With the bezel the whole set is usually about 57 × 33 inches before the stand.
How are TV sizes measured?+
TV sizes are measured diagonally across the visible screen, from one corner to the opposite corner, not including the frame. That is why two 65-inch TVs can have slightly different outer dimensions.
How wide is a 55 inch TV?+
A 55-inch 16:9 screen is about 47.9 inches wide and 27.0 inches tall (about 122 × 68 cm). Allow roughly an extra inch of width for the bezel.
Is a 75 inch TV much bigger than a 65 inch?+
Yes. Although the diagonal grows by only 10 inches, the screen area increases by about 33%, from roughly 1,805 to 2,404 square inches.
What aspect ratio are modern TVs?+
Virtually all modern TVs use 16:9, the HDTV and 4K broadcast standard. Ultrawide 21:9 and 32:9 panels are mostly computer monitors, and 4:3 was used by older tube TVs.