Monitor size is measured diagonally across the screen, corner to corner, in inches

When you see a monitor listed as 24 inches or 27 inches, that number refers to the diagonal distance from one corner of the screen to the opposite corner. It does not measure the width or height alone, and it does not include the plastic bezel or frame around the screen. To measure your own monitor, you need a tape measure or ruler, and you measure from the bottom-left corner of the actual display to the top-right corner (or any opposite corners).

This diagonal measurement is the industry standard worldwide. It exists because older television sets were measured the same way, and the practice stuck. The diagonal tells you roughly how much screen real estate you have, but it does not tell you the full story — a 27-inch ultrawide monitor and a 27-inch standard monitor have the same diagonal but very different widths and heights.

Key Takeaways

  • Monitor size is always the diagonal measurement from corner to corner of the actual display, measured in inches, and does not include the frame.
  • You measure from the bottom-left corner of the screen to the top-right corner (or any two opposite corners) using a tape measure or ruler.
  • The diagonal measurement alone does not tell you the width or height, so two monitors with the same diagonal size can look very different depending on their aspect ratio.
  • If you cannot measure physically, you can find the exact size in your monitor's manual, on the manufacturer's website, or in your computer's display settings.

How to physically measure your monitor

Start with a tape measure or a ruler long enough to span the distance. Place one end at the bottom-left corner of the display itself — the corner where the screen glass or panel begins, not the plastic frame. Stretch the tape diagonally to the top-right corner of the screen and read the measurement in inches. Write down the number to the nearest half-inch or quarter-inch.

If your monitor is mounted on an arm or stand, you may need to angle the tape measure slightly to account for the tilt of the screen. Measure as straight as you can from corner to corner. If the screen is curved, measure along the curve itself rather than trying to measure a straight line through the middle.

The measurement you get should match or come very close to the advertised size. If your 24-inch monitor measures 23.8 inches, that is normal — manufacturers round to the nearest whole number. If it measures significantly different, double-check that you started and ended at the actual screen corners, not the frame.

Finding your monitor size without measuring

If you do not have a tape measure or prefer not to open the monitor's manual, your computer can tell you the size. On Windows, right-click the desktop, select Display settings, and scroll down to find the resolution and refresh rate. The settings page does not always list the diagonal size, but you can look up your monitor model number there and search the manufacturer's website.

To find your monitor model number, look at the back or bottom of the monitor itself — it is usually printed on a sticker or label. You can also check your computer's device manager. On Windows, press Windows key + X, select Device Manager, expand Monitors, and right-click your monitor to view properties. On Mac, go to Apple menu > About This Mac > Displays to see the resolution, though the size may not be listed there.

Once you have the model number, visit the manufacturer's website (Dell, LG, ASUS, HP, etc.) and search for that model. The product page will list the diagonal screen size, along with the width and height if you need those measurements too.

Why diagonal measurement matters less than you might think

Two monitors can have the same diagonal size but very different shapes. A 27-inch ultrawide monitor (usually 21:9 aspect ratio) is much wider and shorter than a 27-inch standard monitor (16:9 aspect ratio). Both measure 27 inches corner to corner, but the ultrawide gives you more horizontal space for spreadsheets or video editing, while the standard monitor is taller relative to its width.

If you are shopping for a new monitor, the diagonal size is a starting point, but you should also look at the aspect ratio (the width-to-height proportion) and the resolution (how many pixels fit on the screen). A 24-inch monitor at 1920 × 1080 pixels looks sharper than a 24-inch monitor at 1366 × 768 pixels because the pixels are smaller and more densely packed.

Common monitor sizes and what they look like

Most desktop monitors fall into a few standard diagonal sizes. A 21-inch or 22-inch monitor is compact and fits small desks; a 24-inch is the most common size for general office and home use; a 27-inch gives noticeably more screen space without taking up too much room; and 32-inch or larger monitors are usually reserved for professional work like video editing or gaming setups where you want to see fine detail from a distance.

Laptop screens are typically smaller — 13-inch, 14-inch, 15-inch, and 17-inch are standard — and are measured the same way, corner to corner. Tablets and phones are also measured diagonally, which is why a 10-inch tablet and a 10-inch monitor are not the same size in real-world use.

What the diagonal measurement does not tell you

The diagonal size does not account for the bezel (the frame around the screen), so two monitors of the same size can take up different amounts of desk space depending on how thick the bezel is. Modern monitors tend to have thinner bezels, but older monitors or budget models may have wider frames.

The diagonal also does not tell you about brightness, color accuracy, refresh rate, or response time — all of which affect how the monitor actually performs. A 27-inch gaming monitor at 144 Hz will feel very different to use than a 27-inch office monitor at 60 Hz, even though they are the same size.

Frequently Asked Questions

Does the monitor size include the plastic frame around the screen?

No. The size measurement is only the diagonal of the actual display panel, not the bezel or frame. If you measure from the outer edge of the plastic frame, you will get a larger number than the advertised size.

Can I measure the width or height instead of the diagonal?

You can measure the width and height if you need them for a desk or mount, but the monitor size itself is always given as the diagonal. If you know the width and height, you can calculate the diagonal using the Pythagorean theorem, but most people just measure corner to corner.

Why do manufacturers use diagonal measurement instead of width?

The diagonal measurement became standard for televisions decades ago and carried over to computer monitors. It is a single number that roughly indicates screen size, though it does not account for aspect ratio or shape.

If my monitor measures 23.8 inches but is labeled 24 inches, is something wrong?

No. Manufacturers round the diagonal measurement to the nearest whole number for marketing purposes. A 23.8-inch monitor is labeled and sold as a 24-inch monitor. This is normal and expected.

How do I know if a monitor will fit on my desk?

Look up the width and height (not the diagonal) on the manufacturer's website or in the manual. The diagonal size alone does not tell you how much desk space the monitor needs. A 27-inch ultrawide is much wider than a 27-inch standard monitor, even though they have the same diagonal.