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

When you buy a monitor, the advertised size — 24 inches, 27 inches, 32 inches — refers to the diagonal distance from one corner of the display to the opposite corner. This measurement includes only the visible screen area, not the plastic bezel or frame around it. You measure in a straight line from the bottom-left corner to the top-right corner (or top-left to bottom-right; the distance is the same either way).

The diagonal measurement is an industry standard because it gives a single number that roughly describes how much screen real estate you have. A 27-inch monitor is noticeably larger than a 24-inch one, but the difference in actual viewing area is bigger than the three-inch gap suggests — the 27-inch has about 27% more screen space. Understanding this helps you choose a monitor that fits your desk and your work.

Key Takeaways

  • Monitor size is always the diagonal measurement from corner to corner of the visible screen, measured in inches.
  • The measurement does not include the plastic frame or bezel around the screen.
  • You can measure with a ruler or measuring tape, or look up the exact dimensions in the monitor's manual or product listing.
  • Aspect ratio (the width-to-height proportion) and resolution (pixel count) are separate from size and affect how much you can fit on screen.
  • If you are replacing a monitor, the diagonal size alone does not tell you whether it will fit your desk — you also need the width and depth measurements.

How to measure with a ruler or tape measure

Turn off the monitor and let it cool for a few minutes if it has been on. Place a ruler or measuring tape at the bottom-left corner of the screen (where the glass or plastic display surface meets the frame) and stretch it diagonally to the top-right corner. Keep the ruler flat against the screen and read the measurement where it reaches the opposite corner. Round to the nearest half-inch or whole inch — manufacturers do the same.

If your monitor is mounted on an arm or stand that makes it hard to reach the corners, you can measure the width and height of the visible screen separately, then use the Pythagorean theorem: multiply width by itself, multiply height by itself, add those two numbers together, and take the square root. For example, a screen that is 21.5 inches wide and 12.1 inches tall would be √(21.5² + 12.1²) = √(462.25 + 146.41) = √608.66 ≈ 24.7 inches diagonally. Most people find a direct diagonal measurement faster.

Where to find the exact measurement without measuring

The easiest route is the monitor's manual or the original product box, both of which list the diagonal screen size. If you no longer have those, check the manufacturer's website — search for your monitor model number (usually printed on the back or bottom of the unit) and look for the specifications or datasheet. The model number is often a combination of letters and numbers like "Dell S2721DGF" or "LG 27UP550".

You can also find the size on the retailer's product page if you remember where you bought it, or on sites like Amazon, Newegg, or Best Buy by searching the model number. The product listing will show the diagonal size prominently, along with the full width, height, and depth of the monitor with its stand — measurements you need if you are deciding whether it will fit your desk.

Why diagonal size does not tell the whole story

Two monitors can have the same diagonal size but very different shapes and usable screen area. A 27-inch monitor in standard 16:9 aspect ratio (wider than it is tall) has different dimensions than a 27-inch ultrawide monitor in 21:9 aspect ratio. The ultrawide is much wider but shorter, so it takes up more desk space horizontally even though the diagonal is the same.

Resolution — the number of pixels displayed — is also separate from size. A 24-inch monitor might have 1920 × 1080 pixels (Full HD) or 2560 × 1440 pixels (2K), and both are called 24-inch. The higher-resolution monitor packs more pixels into the same physical space, making text and images sharper but also smaller on screen. When you are shopping, check the aspect ratio and resolution along with the diagonal size to understand what you are actually getting.

Measuring your desk space before you buy

Knowing the monitor's diagonal size is not enough to know whether it will fit. You need the width and depth of the monitor with its stand attached. Measure the width of your desk or the space where the monitor will sit, then compare it to the monitor's width measurement (not the diagonal). Most monitors list width, height, and depth in the specifications — width is the one that matters most for desk fit.

If you are mounting the monitor on an arm or wall bracket, the stand depth does not matter, but the width still does. Check whether the monitor's base or stand will interfere with a keyboard, mouse pad, or other equipment. Some monitors have narrow stands that take up very little desk space; others have wide bases that extend far forward. The product photos and dimensions will show this.

Common monitor sizes and what they mean

Monitor sizes cluster around a few standard diagonals. A 24-inch monitor is the smallest common size for desktop work and fits most desks comfortably. A 27-inch monitor is popular for gaming and professional work because it offers noticeably more screen space without being unwieldy. A 32-inch monitor is large enough that you may need to sit farther back or move your eyes more to see the whole screen — it works well for video editing, design, or if you sit at a distance from your desk.

Ultrawide monitors (21:9 aspect ratio) typically come in 34-inch or 38-inch diagonal sizes but are much wider than standard monitors of the same size. A 34-inch ultrawide is wider than a standard 38-inch monitor but shorter. If you are replacing a monitor, do not assume a monitor with the same diagonal size will fit the same space — check the width measurement.

Frequently Asked Questions

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

No. The diagonal measurement is only the visible screen area, from the edge of the glass or display surface to the opposite corner. The plastic bezel or frame around the screen is not included in the advertised size.

What is the difference between diagonal size and resolution?

Diagonal size is the physical measurement of the screen in inches. Resolution is the number of pixels displayed (like 1920 × 1080). Two monitors can be the same size but have different resolutions, which affects how sharp the image looks and how much content fits on screen.

Can I use the diagonal size to figure out if a monitor will fit my desk?

Not reliably. You need the width measurement of the monitor with its stand. Two monitors with the same diagonal size can have very different widths — especially if one is ultrawide. Always check the width and depth specifications before buying.

How do I find my monitor's model number?

Look on the back or bottom of the monitor for a label with the manufacturer name and model number. It is usually a combination of letters and numbers. Once you have it, search the manufacturer's website or a retailer to find the full specifications, including diagonal size.

Is a 27-inch monitor twice as big as a 13.5-inch monitor?

No. A 27-inch monitor has roughly four times the screen area of a 13.5-inch monitor, even though the diagonal is only twice as large. Screen area grows with the square of the diagonal, so small differences in size create large differences in usable space.