Case 1
- How long is the diagonal?
- 27in
- Aspect ratio, width part
- 16
- Aspect ratio, height part
- 9
23.53in
Open with these valuesScreen Width Calculator
23.53in
Result: 23.53 inThe diagonal alone does not say how wide a screen is — the aspect ratio decides how it splits. A 27-inch 16:9 panel is 23.53 in wide and 13.24 in tall; a 27-inch 4:3 panel is only 21.6 in wide but 16.2 in tall. Enter the diagonal in any unit and the width comes back in the same one.
Worked examples
Case 2
- How long is the diagonal?
- 55in
- Aspect ratio, width part
- 16
- Aspect ratio, height part
- 9
47.94in
Open with these valuesCase 3
- How long is the diagonal?
- 13.3in
- Aspect ratio, width part
- 16
- Aspect ratio, height part
- 10
11.28in
Open with these valuesHow it's calculated
width = D × w ÷ √(w² + h²)
- StepEnter the diagonal — the number the screen is sold by.
- StepEnter the aspect ratio as two numbers: 16 and 9 for widescreen, 4 and 3 for old panels.
- ResultRead the width; swap the two ratio numbers to get the height instead.
Reference table
| Diagonal, ratio | Height | Width |
|---|---|---|
| 24, 16, 9 | 11.77 in | 20.92 |
| 27, 16, 9 | 13.24 in | 23.53 |
| 27, 4, 3 | 16.20 in | 21.60 |
| 32, 16, 9 | 15.69 in | 27.89 |
| 34, 21, 9 | 13.39 in | 31.25 |
| 55, 16, 9 | 26.96 in | 47.94 |
Questions
How do I get width and height from the diagonal?
Split the diagonal in the proportions of the aspect ratio: width = D × w ÷ √(w² + h²), height = D × h ÷ √(w² + h²). A 27-inch 16:9 screen is about 23.53 in wide and 13.24 in tall.
Why is the diagonal not enough on its own?
Because how it splits depends on the shape. A 27-inch 16:9 panel is wider and shorter than a 27-inch 4:3 panel, even though both are sold as 27 inches.
Which aspect ratio should I enter?
The screen's native one: 16 and 9 for most TVs and monitors, 4 and 3 for older displays and many tablets, 16 and 10 for some laptops, 21 and 9 for ultrawide.
Does it matter whether I use inches or centimetres?
No — the width comes back in whatever unit you entered the diagonal in. The formula is a pure proportion, so inches give inches and centimetres give centimetres.
Is the bezel included?
No. These are the dimensions of the active display area that matches the quoted diagonal, so the device itself is a little larger. Check the manufacturer's sheet before drilling a wall mount.
How do I get the screen area?
Multiply the width by the height. For the 27-inch 16:9 example that is 23.53 × 13.24, about 311.5 square inches — a fairer comparison than the diagonal when two screens have different shapes.
Sources and last check
Information, not professional advice.