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

When someone says a monitor is 27 inches, they mean the distance from the bottom-left corner to the top-right corner (or any opposite corners) measures 27 inches. This diagonal measurement is the standard used by every manufacturer. It's not the width, not the height, and not the frame-to-frame distance—just the glass or panel itself, measured at an angle.

The reason manufacturers use diagonal measurement is historical: it comes from how television screens were sized decades ago, and the industry never changed. What matters for you is that this single number doesn't tell you how wide or tall your monitor actually is. A 24-inch monitor and a 27-inch monitor look noticeably different on a desk, even though the difference sounds small.

Key Takeaways

  • Monitor size is always the diagonal measurement in inches, taken from one corner of the screen to the opposite corner, not including the frame or bezel.
  • You can measure your current monitor yourself with a tape measure or ruler, starting from the bottom-left corner of the glass and going to the top-right corner.
  • The aspect ratio (usually 16:9 or 16:10) determines the actual width and height for any given diagonal size, so two 27-inch monitors can have different dimensions if they have different aspect ratios.
  • If you're buying a new monitor, the size label on the box or product page is the diagonal measurement; you can calculate the width and height using the aspect ratio if you need exact desk space.

How to measure your current monitor with a tape measure

Place the end of a tape measure or ruler at the bottom-left corner of your monitor's screen (the glass itself, not the plastic frame). Stretch it diagonally to the top-right corner. Write down the number where the tape ends. That's your monitor size in inches.

Make sure you're measuring only the visible screen area. Don't include the black border or plastic bezel around the edges. If your monitor has a curved screen, measure along the curve from corner to corner—the tape will follow the surface naturally.

If you don't have a tape measure long enough, you can use a piece of string, mark where it reaches the opposite corner, and then measure the string against a ruler or tape measure on a flat surface.

Understanding aspect ratio and what it means for actual width and height

The aspect ratio is the relationship between a monitor's width and height. The most common ratio is 16:9 (sixteen units wide for every nine units tall). Some monitors use 16:10 or 21:9, which changes how wide or tall the screen appears even if the diagonal size is the same.

For example, two 27-inch monitors with different aspect ratios will have different actual widths and heights. A 27-inch monitor with 16:9 aspect ratio is roughly 23.5 inches wide and 13.2 inches tall. A 27-inch monitor with 16:10 aspect ratio is roughly 23.4 inches wide and 14.6 inches tall. The second one is taller but slightly narrower, even though both are called 27 inches.

If you need to know the exact width and height of a monitor you're considering buying, check the product specifications on the manufacturer's website or retailer page. They will list the width and height in millimeters or inches. You don't need to calculate it yourself unless the specs aren't available.

Why manufacturers don't list width and height instead

Diagonal measurement is simpler to advertise and compare. It's a single number that lets you quickly rank monitors from smallest to largest. Width and height would require two numbers, and they'd vary depending on aspect ratio, making the comparison less straightforward.

From a practical standpoint, diagonal measurement also made sense when monitors were mostly square or nearly square. Modern widescreen monitors are much wider than they are tall, so the diagonal doesn't tell you how much desk space you actually need. That's why checking the width specification matters if you're worried about fitting a monitor into a tight space.

How to find the size of a monitor you don't own yet

If you're shopping for a new monitor, the size is always listed in the product name or specifications. Look for a number followed by "inch" or a quotation mark (27" means 27 inches). This number is the diagonal measurement.

The product page will also show the actual width and height, usually under "Physical Dimensions" or "Specifications." These are the numbers to use if you're checking whether the monitor will fit on your desk or in a specific space. Measure your desk or shelf first, then compare it to the width and height listed in the specs—not the diagonal size.

If you're buying a used monitor and the size isn't labeled, you can measure it yourself with a tape measure using the same method described above.

Common monitor sizes and what they look like on a desk

Most office and home monitors fall into a few standard sizes. A 21-inch or 22-inch monitor is compact and fits easily on a small desk. A 24-inch monitor is the most common size for general use—it's large enough to work comfortably but doesn't dominate a standard desk. A 27-inch monitor is noticeably larger and is popular for gaming, photo editing, and detailed work. A 32-inch monitor is quite large and works best on a spacious desk or when you sit farther back.

The jump from 24 inches to 27 inches might sound small, but the screen area increases by about 30 percent. The jump from 27 inches to 32 inches is another 40 percent increase in area. If you're upgrading, sit in front of a monitor at a store or a friend's house to see how the size feels in practice. What looks good in a photo might feel cramped or overwhelming at your actual desk distance.

Measuring ultra-wide monitors

Ultra-wide monitors—those with a 21:9 or even wider aspect ratio—are measured the same way: diagonally from corner to corner. A 34-inch ultra-wide monitor is 34 inches from bottom-left to top-right, just like a standard 34-inch monitor would be. The difference is that the ultra-wide is much wider and less tall than a standard 16:9 monitor of the same diagonal size.

Ultra-wide monitors take up significantly more horizontal desk space, so if you're considering one, pay close attention to the width specification. A 34-inch ultra-wide might be 31 inches wide or more, which is wider than many standard desks. Measure your desk space before buying.

Frequently Asked Questions

Is the monitor size the same as the screen size?

Yes. Monitor size and screen size refer to the same diagonal measurement. The frame or bezel around the screen doesn't count toward the size. When a monitor is labeled 27 inches, that's the diagonal of the visible glass or panel only.

Can I measure from the top-left to the bottom-right instead of bottom-left to top-right?

Yes. Any diagonal corner-to-corner measurement gives the same result. Top-left to bottom-right, bottom-left to top-right—they're the same distance. Pick whichever is easier to reach with your tape measure.

Do I need to include the monitor stand or base in the measurement?

No. Measure only the screen itself. The stand, base, and frame are not part of the size measurement. Only the diagonal of the visible display area counts.

What if my monitor has a curved screen?

Measure along the curve from corner to corner. The tape measure or string will naturally follow the curved surface. The diagonal measurement is still the standard, even for curved monitors.

Why does my 27-inch monitor look smaller than my friend's 27-inch monitor?

The most likely reason is aspect ratio. If yours is 16:10 and theirs is 16:9, theirs will look wider and shorter, which can make it appear larger overall. Another possibility is that you sit farther away from your monitor, which makes it look smaller. The actual diagonal size is the same, but the shape and your viewing distance affect how large it appears.