How to Measure a TV or Monitor Screen Size

A screen’s size is the length of its diagonal: a straight line from one corner of the picture to the opposite corner. It doesn’t include the frame (the bezel) or the stand. That’s true for TVs, computer monitors, laptops, tablets and phones alike, and it’s why a “55-inch” TV is nowhere near 55 inches wide.

How to measure a screen

1. Turn the screen off so you can see exactly where the picture area ends.
2. Hook a tape measure on the bottom-left corner of the visible screen, not the edge of the frame.
3. Stretch it to the top-right corner of the visible screen and read the length in inches. Round to the nearest inch for a TV, or the nearest tenth for a laptop.
4. For width and height, measure straight across and straight up the visible area the same way.

A soft tape measure is easiest. With a rigid one, keep it clear of the screen surface, because pressing on some panels can damage them. If you’re measuring a laptop, the screen is usually 13–16 inches, so a 12-inch ruler won’t reach corner to corner. Measure the width and height instead and let the screen size calculator work out the diagonal.

Width and height from the diagonal

Screens are sold by diagonal, but what decides whether one fits a space is its width and height. Those depend on the shape, or aspect ratio. Almost every TV and most monitors are 16:9, which gives:

• width = 0.872 × diagonal
• height = 0.490 × diagonal

TV size	Screen width	Screen height	Sit at least (30°)	Cinema-like (40°)
32″	27.9 in (71 cm)	15.7 in (40 cm)	4.3 ft	3.2 ft
43″	37.5 in (95 cm)	21.1 in (54 cm)	5.8 ft	4.3 ft
50″	43.6 in (111 cm)	24.5 in (62 cm)	6.8 ft	5.0 ft
55″	47.9 in (122 cm)	27.0 in (68 cm)	7.5 ft	5.5 ft
65″	56.7 in (144 cm)	31.9 in (81 cm)	8.8 ft	6.5 ft
75″	65.4 in (166 cm)	36.8 in (93 cm)	10.2 ft	7.5 ft
85″	74.1 in (188 cm)	41.7 in (106 cm)	11.5 ft	8.5 ft

The last two columns are the seating distances at which the screen fills 30° and 40° of your view. 30° is the minimum SMPTE recommends for a home screen, and about 40° is the more immersive figure THX recommends. Sitting anywhere between the two is a sensible range; with a 4K TV you can sit at the closer end without seeing pixels.

Monitors and laptops

Monitors and laptops come in more shapes, so work out the width from the right ratio:

• 24″ 16:9 monitor: 20.9 × 11.8 in (53 × 30 cm)
• 27″ 16:9 monitor: 23.5 × 13.2 in (60 × 34 cm)
• 34″ 21:9 ultrawide: 31.3 × 13.4 in (79 × 34 cm)
• 14″ 16:10 laptop: 11.9 × 7.4 in (30 × 19 cm)

On a Mac, the built-in screen size is listed under Apple menu → About This Mac. Windows doesn’t show the physical size, but you can find it from the model number, or open our screen size calculator on that screen, calibrate it with a bank card, and read its size directly.

Will it fit? Measure the TV, not just the screen

The table above is the picture area. The TV itself is wider and taller by the frame, typically a few millimeters to about an inch on each side on modern sets, and the stand adds height and needs its own depth. Before buying a TV for a cabinet or a niche:

1. Look up the maker’s dimensions without stand (width × height × depth).
2. Measure the space, and leave at least 1–2 inches around the TV for air to flow.
3. For a TV on its stand, check the stand footprint. Some stands sit at the ends of the TV, so they need a surface nearly as wide as the TV itself.

Screen size and pixel density

Two screens of the same size can look very different in sharpness. Pixel density (PPI) tells you how tightly the pixels are packed: divide the diagonal resolution by the diagonal size. A 27-inch 2560 × 1440 monitor has √(2560² + 1440²) = 2937 pixels on the diagonal, so 2937 ÷ 27 = 109 PPI. A 27-inch 4K (3840 × 2160) monitor has 163 PPI. The screen size calculator does this for you when you add the resolution, and pixels to inches converts sizes at any pixel density.