Screen Sizes Explained: Diagonal, Width and Height for Every Device

How screen size is measured

Every screen, from a phone to a projector screen, is sold by the length of the diagonal of its visible picture. The bezel or frame is not included. The convention comes from early round picture tubes, which were sized by their diameter. When tubes became rectangular, the diagonal took the diameter's place, and the habit carried over to flat panels.

The diagonal alone does not tell you the shape. Two screens with the same diagonal can be very different in width and height, depending on the aspect ratio (the ratio of width to height). A 34-inch ultrawide monitor and a 34-inch 16:9 monitor share a diagonal but not a height: 13.2 in against 16.7 in.

• Visible area only. Measure from the corner of the lit picture to the opposite corner, not from frame corner to frame corner.
• "Class" sizes. TVs are often sold as a size class. A "65-inch class" TV may measure 64.5 in, and a "75-inch class" 74.5 in. The rounding is usually under half an inch.
• Rounded corners and notches. Phones and some tablets measure the diagonal as if the corners were square. The actual lit area is slightly smaller.

Width and height from the diagonal

For a screen with aspect ratio a:b and diagonal d, Pythagoras gives width = d × a ÷ √(a² + b²) and height = d × b ÷ √(a² + b²). In practice you only need the two factors for each ratio.

"21:9" monitors are actually 64:27 (3440 × 1440 or 2560 × 1080 pixels, a ratio of about 2.37:1); the factors above use the true ratio. For a deeper look at where these ratios come from, see the aspect ratio guide.

Screen sizes by device

Each device category has its own standard sizes and usually its own aspect ratio. The table gives the range sold today and the width and height of a typical size.

Phone screens are sized with the phone held upright, so the "width" above is the long side. Laptop sizes are covered model by model in the laptop size guide, including the 13.3, 14, 15.6 and 16-inch formats.

Screen dimensions chart: common sizes in inches and cm

For every TV size from 32 to 98 inches, with real model dimensions and weights, see the TV size chart. Monitors from 21.5 to 49 inches are in the monitor size guide.

34-inch 21:9 31.3 × 13.2 in32-inch 16:9 27.9 × 15.7 in27-inch 16:9 23.5 × 13.2 in

Comparing screens with different aspect ratios

Because diagonal hides shape, the fair comparison between screens of different ratios is height or area, not diagonal.

• Same height: a 34-inch 21:9 monitor (13.2 in tall) is a wider 27-inch 16:9 monitor. A 49-inch 32:9 (13.3 in tall) is two 27-inch monitors side by side.
• Same area: a 14-inch 16:10 laptop has 88 sq in of screen; a 15.6-inch 16:9 laptop has 104 sq in, 18% more, although the diagonals differ by only 1.6 in.
• Movies on a 16:9 TV: a 2.39:1 film fills the full width but only 74% of the height, leaving black bars top and bottom. On a 65-inch TV the film image is 56.7 × 23.7 in.
• 4:3 content on 16:9: old TV shows fill the height but only 75% of the width, with bars at the sides.

The area of a screen grows with the square of the diagonal. Going from a 55 to a 65-inch TV is an 18% increase in diagonal but a 40% increase in area, which is why a "10 inches bigger" TV looks so much larger on the wall.

Screen size vs resolution and pixel density

Resolution is the number of pixels; screen size spreads them over a larger or smaller area. Pixel density, in pixels per inch (PPI), is the diagonal pixel count divided by the diagonal in inches: √(width² + height²) ÷ diagonal.

The last column is the distance at which one pixel covers one arcminute of vision, the usual threshold for 20/20 eyesight. Sit farther than that and the extra resolution of a denser screen is hard to see. That is why a 65-inch 4K TV looks sharp from a sofa while a 27-inch monitor at desk distance benefits from 1440p or 4K.

How to measure a screen

1. Find the lit area. Turn the screen on with a bright image so you can see where the picture ends inside the bezel.
2. Measure corner to corner. Run a tape from the bottom-left corner of the picture to the top-right. That is the diagonal; compare it with the advertised size.
3. Measure width and height. Measure the picture's horizontal and vertical edges. Dividing width by height gives the aspect ratio (1.78 for 16:9, 1.6 for 16:10).
4. For space planning, measure the outside. Furniture, mounts and bags care about the whole device, frame included. On modern TVs the frame adds only 0.2 to 1 in to the width; on current laptops the body is roughly 0.5 to 1.5 in wider than the screen.

Screen sizes in centimeters

Outside the US, screen sizes are often given in centimeters as well as inches. Multiply the inch figure by 2.54. Rounding conventions vary, so the same TV can appear as 139 or 140 cm.

Need to convert other measurements? The unit converter handles inches, centimeters and feet.

Frequently asked questions