Screen Size Converter (TV & Monitor)
Enter a screen's diagonal size in inches and its aspect ratio to get the real width and height in inches and centimeters — plus the diagonal in cm, screen area, and a side-by-side size comparison.
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Note: This calculates the panel (display area) only. Real products add a bezel and stand, so the overall product is slightly larger. One inch equals 2.54 cm; width and height are derived from the diagonal and aspect ratio using the Pythagorean theorem.
How to use it
How this screen size converter works
Toolssok's screen size converter tells you the real width and height of a TV or monitor from the diagonal inches printed on the box. A screen's advertised size is always the diagonal — the distance across the panel from one corner to the opposite corner — so two screens with the same diagonal can still be a very different shape once you account for aspect ratio. This tool turns that single diagonal number, plus the aspect ratio, into the actual width and height in inches (with centimeters alongside), so you can check whether a screen fits your desk, wall, or media cabinet before you buy.
Three steps
First, enter the screen's diagonal size in inches — the number in the product name, such as the 55 in "55-inch TV." Second, pick the aspect ratio; almost every modern TV and most monitors use 16:9, while ultrawide monitors use 21:9 or 32:9. Third, press Calculate width & height to see the real width and height in inches and centimeters, the diagonal in centimeters, and the total screen area.
The formula
Width and height come from the Pythagorean theorem. If the aspect ratio is width:height = w:h, the diagonal expressed in the same units is √(w² + h²). Dividing the diagonal size by that number gives a scale factor, and multiplying it by w and by h gives the real width and height.
Width = Diagonal × w ÷ √(w² + h²)
Height = Diagonal × h ÷ √(w² + h²)
Take a 27-inch 16:9 monitor. √(16² + 9²) = √(256 + 81) = √337 ≈ 18.36. Width = 27 × 16 ÷ 18.36 ≈ 23.5 inches (about 59.8 cm), and height = 27 × 9 ÷ 18.36 ≈ 13.2 inches (about 33.6 cm). The diagonal itself converts to centimeters at 27 × 2.54 ≈ 68.6 cm, using the international standard that one inch equals exactly 2.54 cm, fixed by the 1959 international yard-and-pound agreement.
Because 16:9 is so common, the math simplifies further: multiply the diagonal by 0.872 for the width in inches and by 0.49 for the height, then by 2.54 again for centimeters. A 21:9 ultrawide monitor uses the same formula with w=21 and h=9, which is why a 34-inch 21:9 monitor is noticeably wider but shorter than a 34-inch 16:9 screen would be.
Good to know
Screen area grows much faster than the diagonal, because area scales with the diagonal squared. Going from a 55-inch TV to a 65-inch TV is only an 18% longer diagonal, but the screen area increases by about 40%. That is why a jump of just 10 inches can look like a much bigger difference than the number alone suggests. Manufacturers also round the advertised diagonal to the nearest whole inch, so the true panel can be a fraction of an inch smaller than the number on the box. The table below shows the real width and height for common 16:9 sizes; add a couple of inches on each side for the bezel and stand when you plan your space.
| Diagonal | Width | Height |
|---|---|---|
| 24" | 20.9" (53.1 cm) | 11.8" (29.9 cm) |
| 27" | 23.5" (59.8 cm) | 13.2" (33.6 cm) |
| 32" | 27.9" (70.8 cm) | 15.7" (39.9 cm) |
| 43" | 37.5" (95.2 cm) | 21.1" (53.6 cm) |
| 55" | 48.0" (121.8 cm) | 27.0" (68.5 cm) |
| 65" | 56.7" (143.9 cm) | 31.9" (80.9 cm) |
Recommended TV size by room
The right screen size depends more on how far you sit than on the room's square footage. As a rough starting point, many home-theater guides suggest a viewing distance of about 1.5 to 2.5 times the screen's diagonal for an FHD (1080p) set, and a closer 1 to 1.5 times the diagonal for 4K, since the extra pixel density still looks sharp up close.
| Viewing distance | FHD recommended | 4K recommended |
|---|---|---|
| Under 5 ft (1.5 m) | 32-40" | 40-50" |
| 5-6.5 ft (1.5-2 m) | 43-50" | 50-60" |
| 6.5-8 ft (2-2.5 m) | 50-55" | 60-70" |
| 8 ft or more (2.5 m+) | 55-65" | 75" or larger |
55, 65 and 75 inches are among the most widely stocked TV sizes at US electronics retailers, largely because they suit typical living-room seating distances of about 8 to 12 feet. For a home office or bedroom where the screen sits closer, a 43- to 50-inch TV or a 27- to 32-inch monitor is usually plenty. For an exact figure based on your own seating distance, the viewing distance calculator works out the ideal range for you.
16:9 vs. ultrawide: which aspect ratio should you pick?
Almost every TV sold today is 16:9, the aspect ratio standardized for digital broadcast (ATSC in the US, DVB elsewhere) and used by virtually all streaming video, so there is rarely a reason to look elsewhere for a television. Desktop monitors have more variety. A standard 16:9 monitor, typically 24 to 32 inches, suits general use, office work and most games. A 21:9 ultrawide trades some height for extra width, which works well for video editing timelines, spreadsheets and cinematic games designed with wide framing in mind, though black bars can appear when watching standard 16:9 video. A 32:9 super-ultrawide is roughly equivalent to two 16:9 monitors placed side by side without a bezel in between, but it needs considerable desk depth to sit at a comfortable viewing distance.
Frequently asked questions
Where exactly is a screen's diagonal measured?
The diagonal is the straight-line distance across the visible display area, from one corner to the opposite corner — not the width, the height, or the outer case. Since one inch equals 2.54 cm, a 55-inch screen has a diagonal of about 139.7 cm regardless of its aspect ratio.
Why do two screens with the same diagonal have different widths?
Because the diagonal alone does not describe a shape — the aspect ratio does. A 27-inch 16:9 monitor is about 23.5 inches wide, while a 27-inch 21:9 ultrawide with the same diagonal would be wider and shorter. Enter both ratios into this converter to see the width and height change side by side.
Does the calculated size match the manufacturer's listed dimensions?
This converter calculates the panel — the active display area — only. Real products add a bezel and, for TVs, a stand, so the packaged product measures slightly more than these numbers. Manufacturers also round the diagonal to the nearest whole inch, which can shift the result by a fraction of an inch. Leave 1 to 2 inches of extra width when planning tight furniture spaces.
How much bigger is a 65-inch TV than a 55-inch TV?
At 16:9, a 55-inch TV is about 48.0 inches wide and a 65-inch TV is about 56.7 inches wide — roughly 8.7 inches more. The diagonal is only 18% longer, but because area scales with the diagonal squared, the screen area ends up about 40% larger.
Is a 27-inch or 32-inch monitor the better choice?
At 16:9, a 27-inch monitor is about 23.5 inches wide and a 32-inch monitor is about 27.9 inches wide, a difference of roughly 4.4 inches. Turn on Compare with another screen above to see the exact width, height and area difference for your own numbers — the area difference is usually larger than the width difference alone suggests, since both dimensions grow together.
What TV size fits my room?
As a starting point, look at your seating distance rather than the room's total size: about 32 to 40 inches for under 5 feet, 43 to 55 inches for 5 to 8 feet, and 55 to 75 inches or larger beyond 8 feet, with 4K screens comfortably supporting the larger end of each range. For an exact figure based on your seating distance, use the viewing distance calculator.
Does this work for laptops, tablets and phones too?
Yes. Any screen's real width and height can be calculated from its diagonal and aspect ratio the same way. Laptops are commonly 16:9 or 16:10, tablets are often close to 4:3, and phones usually have a tall ratio such as 19.5:9 or 20:9 — check the device's spec sheet for its exact ratio before entering it.
Related tools
Source: one inch equals exactly 2.54 cm under the 1959 international yard-and-pound agreement. 16:9 is the standard for digital television (ATSC/DVB) and virtually all streaming video; the other ratios shown are common alternatives used in monitors. Calculations use the panel (display area) only — check the manufacturer's specification for bezel and stand dimensions. All calculations run in your browser only.