Screens, panels and televisions are sold by diagonal, which tells you remarkably little on its own. The diagonal is the root of the sum of the squares of the sides, so two displays with the same diagonal can have very different widths, heights and areas depending on their aspect ratio.
This is why a 27 inch 16:9 monitor and a 27 inch 21:9 ultrawide are not comparable. The ultrawide is wider but much shorter, and it has noticeably less screen area. Working the sides back from the diagonal and the ratio is the only way to compare them honestly, and this page does that in both directions.
The actual width, height and area for common panels table follows the calculator: 8 rows spanning 13.3 in through 55 in, there so the result can be cross-checked against a value you already trust. The page opens with diagonal already set to 27 in, so there is a finished result on screen before anything is typed. The result is also read against 4 bands, from small panel at the low end to very large panel at the high end, each with a note on what that range means in practice. Box Diagonal Calculator and Circumference to Diameter Calculator are the nearest neighbours to this one.
The formula
w- Width
h- Height
d- Diagonal
Aspect ratio- Width divided by height
How to use this calculator
- Enter the diagonal you are working from.
- Enter the aspect ratio as a width and a height figure, such as 16 and 9.
- The gauge shows the actual width.
- The height, the area and the ratio check appear below.
Worked examples
A 27 inch 16:9 monitor
The height is 27 ÷ root(1 + (16/9) squared) = 13.2371 inches and the width is 23.5325. The area comes to 311.50 square inches.
The same diagonal as a 21:9 ultrawide
The height drops to 10.6358 inches and the width grows to 24.8169. The area falls to 263.95 square inches, about 15.3% less.
Checking the 27 in row
The reference table lists Diagonal = 27 in, giving Ratio: 21:9, Width: 24.82, Height: 10.64, Area (sq in): 263.9. Entering that above should reproduce the same figures — if it does not, the input is being read differently to the way the table assumes.
How to read your score
Frequently asked questions
Why do two screens of the same size differ in area?
Because the diagonal alone does not fix the shape. For a given diagonal, the closer the aspect ratio is to square, the more area you get.
Which aspect ratio gives the most area for a given diagonal?
A square, 1:1. Area falls steadily as the panel gets more elongated, which is why ultrawides have less screen than their diagonal suggests.
How do I compare a 4:3 and a 16:9 screen fairly?
Compare areas rather than diagonals. A 4:3 panel of the same diagonal has about 11% more area than a 16:9 one.
Is the diagonal measured to the bezel or the glass?
Standards specify the active image area, corner to corner. Older marketing sometimes measured the tube or the housing, which is why very old sets seem larger than they view.
What do the bands under the width mean?
They label the figure so it can be read without a reference point of your own: Small panel from 0 to 12; Medium panel from 12 to 24; Large panel from 24 to 48; Very large panel from 48 upwards. The band is a reading aid only — the number itself is exact, and a value sitting just over a boundary is not meaningfully different from one just under it.
What formula does the Rectangle Diagonal Calculator use?
It computes d = √(w^2 + h^2), where w is width; h is height; d is diagonal; Aspect ratio is width divided by height. The same expression is printed on the page above the inputs, so the result can be reproduced by hand or in a spreadsheet.
Screen dimensions by diagonal and aspect ratio
| Diagonal | Ratio | Width | Height | Area (sq in) |
|---|---|---|---|---|
| 13.3 in | 16:10 | 11.28 | 7.05 | 79.5 |
| 15.6 in | 16:9 | 13.60 | 7.65 | 104.0 |
| 24 in | 16:9 | 20.92 | 11.77 | 246.1 |
| 27 in | 16:9 | 23.53 | 13.24 | 311.5 |
| 27 in | 21:9 | 24.82 | 10.64 | 263.9 |
| 32 in | 16:9 | 27.89 | 15.69 | 437.6 |
| 34 in | 21:9 | 31.25 | 13.39 | 418.6 |
| 55 in | 16:9 | 47.94 | 26.96 | 1292.6 |
Both 27 inch rows have the same diagonal but very different areas.