What this calculator covers
- The diagonal, width, height and area of a flat screen from any one of them and its aspect ratio, each in inches, centimeters and millimeters.
- Aspect ratio presets 16:9, 16:10, 21:9, 32:9, 4:3, 3:2, 1:1, 2.39:1 and 9:16, or any custom ratio.
- Two screens side by side, with the difference in width, height, diagonal and area in percent.
- Seating distances for a screen, and screen sizes for a seating distance, with the standard behind each one.
- Sizes greater than 0 and up to 1,000,000 in the chosen unit, and viewing distances up to 10,000.
- Flat screens only. The numbers describe the picture area; the bezel and stand are not included.
- Everything runs in your browser. No sign-up, no login, no pop-ups.
- This page is about physical size. For pixels per inch, use the PPI calculator.
How screen size is calculated
Diagonal, width, height and area
With the aspect ratio r = ratio width ÷ ratio height: height = diagonal ÷ √(r² + 1) and width = r × height. For a 55-inch 16:9 screen that is 55 ÷ √((16 ÷ 9)² + 1) = 26.96 in high and 47.94 in wide.
From the width: height = width ÷ r. From the height: width = r × height. From the area: height = √(area ÷ r) and width = r × height. Then diagonal = √(width² + height²) and area = width × height.
Inches are converted with 1 in = 2.54 cm = 25.4 mm, and areas with 1 in² = 6.4516 cm² = 645.16 mm².
Comparing two screens
Difference = (screen B ÷ screen A − 1) × 100, for width, height, diagonal and area. Area grows with the square of the diagonal, so a 65-inch screen of the same ratio has about 40% more area than a 55-inch one, although its diagonal is only 18% longer.
Viewing distance
A seat that sees the screen width at an angle θ is at distance = width ÷ (2 × tan(θ ÷ 2)). The page gives three angles:
- 30°: the field of view widely quoted as the SMPTE (Society of Motion Picture and Television Engineers) recommendation. For a 55-inch 16:9 screen it is 7.45 ft.
- 40°: the view angle THX recommends as the best seat.
- 28°: the far end of the seating range THX gives, used here for the farthest seat.
The 1080p and 4K UHD lines use 20/20 vision, defined as resolving two points one minute of arc (1′) apart. One row of pixels spans 1′ at height × 3,437.75 ÷ rows, where 3,437.75 = 1 ÷ tan 1′: about 3.2 picture heights for 1080 rows and 1.6 for 2,160 rows. Farther away than that, the pixel rows blend together.
With a viewing distance entered, the page runs the same formulas the other way for screen A's aspect ratio: the diagonal that fills 30° and 40° at that distance, and the largest 1080p and 4K UHD screen whose pixel rows still blend there.
Rounding
Lengths, areas, distances and percentages are shown to 2 decimal places and the decimal ratio to 3, with halves rounded away from zero. Every result is calculated from unrounded numbers, and the unrounded diagonal, width, height and area are always shown, so the same inputs always give the same answer.
FAQ
How wide is a 55-inch TV?
A 55-inch 16:9 screen is 47.94 in (121.76 cm) wide and 26.96 in (68.49 cm) high. Choose another ratio or diagonal above for other screens.
How do I measure a screen size?
Screen size is the diagonal of the picture area, from one corner to the opposite corner, without the bezel. If you can only measure the width or the height, choose that under "I know the" and the calculator works out the diagonal.
How big is a TV by area?
Choose Area under "I know the" to go from an area to the diagonal, or read the area line of any result. Comparing two screens also gives the difference in area.
How far should I sit from my TV?
Enter the screen and read the seat distances: 30° is the SMPTE figure, 40° and 28° are the THX best seat and farthest seat. Enter your own distance to see which screen size fits it.
Does this work for monitors, laptops and phones?
Yes. Any flat screen works: pick its ratio, or type a custom one, and enter any one dimension. For a screen held in portrait, use 9:16.
Can it tell me the pixel density?
No, this page works with physical sizes only. The PPI calculator gives pixels per inch from a screen's resolution and diagonal.