TVs, monitors, laptops and phones are sold by their diagonal, which says surprisingly little about how wide a screen is or how big the picture looks. This calculator turns a diagonal and an aspect ratio into the actual width, height and viewing area, in inches and centimeters. Tick Compare to put a second screen next to it and see the real difference in area.
How to use the screen size calculator
- Enter the diagonal size and choose inches or centimeters.
- Pick the aspect ratio: 16:9 for nearly all TVs and most monitors, 16:10 or 3:2 for many laptops, 21:9 for ultrawides, or a custom ratio.
- Optionally tick Compare with a second screen and enter its diagonal and ratio.
- Read the width and height on the tape. The outline below is drawn to scale.
Screen size formulas
For a diagonal d and an aspect ratio rw:rh:
These come straight from the Pythagorean theorem: the width, height and diagonal form a right triangle whose sides are in the ratio rw : rh : √(rw² + rh²).
Worked example
A 65-inch 16:9 TV:
- Ratio diagonal: √(16² + 9²) = √337 ≈ 18.3576.
- Width: 65 × 16 ÷ 18.3576 ≈ 56.65 in (143.9 cm).
- Height: 65 × 9 ÷ 18.3576 ≈ 31.87 in (80.9 cm).
- Area: 56.65 × 31.87 ≈ 1,805 square inches.
Compared with a 55-inch 16:9 TV (47.94 × 26.96 in, about 1,293 square inches), the 65-inch screen has 39.7% more area, even though its diagonal is only 18% longer.
Common TV sizes (16:9)
| Diagonal | Width | Height | Area vs. 55″ |
|---|---|---|---|
| 43″ | 37.5 in | 21.1 in | 61% |
| 50″ | 43.6 in | 24.5 in | 83% |
| 55″ | 47.9 in | 27.0 in | 100% |
| 65″ | 56.7 in | 31.9 in | 140% |
| 75″ | 65.4 in | 36.8 in | 186% |
| 85″ | 74.1 in | 41.7 in | 239% |
Because area grows with the square of the diagonal, each step up the size ladder adds more picture than the number suggests.
Choosing a screen size
Viewing distance
A common guideline for 4K TVs is to sit about 1 to 1.5 times the diagonal away, so a 65-inch set suits a seating distance of roughly 5½ to 8 feet. Sit closer with a high-resolution screen and the picture fills more of your view; sit too close with a low-resolution one and you start to see pixels. The PPI calculator works out the distance at which pixels disappear.
Fitting the space
The screen dimensions here exclude the frame. Modern TVs have thin bezels, but add an inch or so to each dimension, plus the stand’s footprint, when measuring a cabinet or wall niche.
Comparing different shapes
Ultrawide monitors are measured diagonally too, so a 34-inch 21:9 monitor is about as tall as a 27-inch 16:9 monitor but much wider. Use the compare option with different ratios to check heights before replacing a monitor in a multi-screen setup.
To work with pixel dimensions instead of inches, try the aspect ratio calculator.
Frequently asked questions
How wide is a 65-inch TV?
The screen of a 65-inch 16:9 TV is about 56.7 inches wide and 31.9 inches tall. The whole TV is slightly larger because of the bezel and stand, so check the manufacturer's spec sheet before buying furniture.
How do you get width and height from the diagonal?
Divide the diagonal by √(rw² + rh²), the diagonal of the ratio, then multiply by each part of the ratio. For 16:9, √(16² + 9²) ≈ 18.358, so a 65-inch screen is 65 × 16 ÷ 18.358 ≈ 56.65 inches wide.
Is a 75-inch TV much bigger than a 65-inch?
Yes. Area grows with the square of the diagonal, so a 75-inch screen has (75 ÷ 65)² ≈ 1.33 times the area of a 65-inch screen with the same aspect ratio — about 33% more picture, not 15%.
Why does a 4:3 screen look smaller than a 16:9 screen with the same diagonal?
For a fixed diagonal, a squarer shape has more area, but widescreen video must be letterboxed on it. A 55-inch 4:3 screen shows 16:9 video at about 44 inches wide, while a 55-inch 16:9 screen shows it at about 48 inches.