What this calculator does
Screens are sold by diagonal, which tells you almost nothing about how big the picture actually is. A 27 inch 16:9 monitor is 23.5 by 13.2 inches, and its area is 311 square inches. The diagonal alone cannot give you either figure without the aspect ratio.
The area comparison is where the surprises are. A 43 inch screen has 790 square inches against 311 for a 27 inch, which is two and a half times the picture for 59% more diagonal. Screen area grows with the square of the diagonal, so the step up between sizes is larger than the numbers suggest.
The formula
The aspect ratio is the original width divided by the height, reduced to its simplest form using the greatest common divisor. Physical screen width is the diagonal multiplied by the ratio divided by the square root of the ratio squared plus one, which follows from Pythagoras. Height is the width divided by the ratio, and pixel density is the horizontal pixel count divided by the physical width.
| Term | Meaning |
|---|---|
| Aspect ratio | Width to height, such as 16:9. Independent of physical size. |
| Diagonal | Corner to corner, which is how screens are marketed and the least informative single measurement. |
| Pixel density (ppi) | Pixels per inch. Higher means finer detail at the same viewing distance. |
| Screen area | The figure that actually describes how much picture there is, and it grows with the square of the diagonal. |
The inputs explained
| Field | What to enter |
|---|---|
| Original width | Original width in pixels, used for the aspect ratio and the pixel density. |
| Original height | Original height in pixels. |
| New width | A new width to scale to, for the proportional resize figure. |
| Screen diagonal (inches) | Screen diagonal in inches. |
When to use it
Comparing two monitor sizes
The area figure shows how much more picture a larger screen actually gives, which the diagonal comparison understates considerably.
Checking pixel density before buying
A 1920 wide panel at 27 inches gives 81.6 ppi, which is noticeably coarser than the same resolution at 24 inches. Density is what determines whether text looks sharp.
Resizing an image proportionally
Entering an original size and a target width gives the height that preserves the proportions, which avoids stretching.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What are the real dimensions of each screen size?
A range of diagonal sizes on a 16:9 panel.
| Diagonal | Screen width × height | Screen area | Pixel density |
|---|---|---|---|
| 24 in | 20.9″ × 11.8″ | 246.1 in² | 91.8 ppi |
| 27 in | 23.5″ × 13.2″ | 311.5 in² | 81.6 ppi |
| 32 in | 27.9″ × 15.7″ | 437.6 in² | 68.8 ppi |
| 43 in | 37.5″ × 21.1″ | 790.1 in² | 51.2 ppi |
Questions
How wide is a 27 inch monitor?
About 23.5 inches for a 16:9 panel, with a height of 13.2 inches. An ultrawide 21:9 panel of the same diagonal would be wider and shorter. The diagonal is meaningless without the aspect ratio, which is why both are needed.
Why does screen area grow so fast?
Because it depends on the square of the diagonal. Going from 27 to 43 inches is 59% more diagonal and 154% more area. This is also why the price gap between sizes is steeper than the diagonal difference implies.
What pixel density do I need?
Around 90 to 110 ppi is comfortable for a desktop monitor at normal viewing distance. Below about 80 the pixel structure becomes visible in text. Higher density screens above 200 ppi generally need operating system scaling to keep interface elements a usable size.
Does a bigger screen always show more?
Only if the resolution rises with it. A 32 inch 1080p panel shows exactly the same content as a 24 inch 1080p one, just larger and coarser. More working space requires more pixels, not more inches.
For ratio arithmetic without the physical dimensions, see the aspect ratio calculator. For viewing distance, see the screen viewing distance calculator.