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

When someone says they have a 27-inch monitor, they mean the distance from the bottom-left corner to the top-right corner of the screen is 27 inches. That diagonal measurement is the standard way manufacturers label monitors, and it is the number you will see on the box and in product listings. The measurement includes only the visible screen area — not the plastic bezel or stand.

This diagonal method exists because it is the fastest way to compare screen sizes at a glance. A 24-inch monitor and a 27-inch monitor look noticeably different when you put them side by side, but the difference is easier to understand as a single number than as separate width and height measurements.

Key Takeaways

  • Monitor size is always the diagonal measurement in inches, taken from corner to corner of the visible screen.
  • You can measure your own monitor with a tape measure or ruler, starting at the bottom-left corner and stretching to the top-right corner.
  • The bezel (plastic frame around the screen) and the stand do not count toward the size measurement.
  • If you cannot measure physically, check your monitor's manual, the manufacturer's website, or the original receipt or box.
  • Common monitor sizes are 21.5, 24, 27, 32, and 34 inches, though sizes vary by brand and model.

How to measure with a tape measure or ruler

Place your tape measure or ruler at the bottom-left corner of the screen itself, where the image actually begins. Do not start at the plastic frame. Stretch the tape diagonally across to the top-right corner of the screen. Write down the number where the tape ends. That is your monitor size in inches.

If your monitor is mounted on an arm or wall, you may need to angle the tape carefully to avoid the stand. A flexible fabric tape measure works better than a rigid ruler for this reason. Make sure the screen is not tilted or angled in a way that would throw off your measurement — ideally, measure when the monitor is sitting flat and level.

Round to the nearest half-inch if your measurement falls between standard sizes. Manufacturers use standard sizes (24, 27, 32 inches), so if you measure 26.8 inches, your monitor is almost certainly a 27-inch model.

Finding the size without measuring

The easiest way to find your monitor size without a tape measure is to check the original box or manual. The size is printed on the front of the box and listed in the specifications section of the manual. If you no longer have either, look at your receipt or invoice from when you bought it — the monitor size should be listed there.

You can also find the size on the manufacturer's website. Look up your monitor's model number (usually printed on the back of the monitor or on a sticker underneath) and search for it on the brand's support page. Dell, LG, ASUS, HP, and other major manufacturers list full specifications including screen size for every model they make.

If you bought the monitor secondhand and have no documentation, take a photo of the model number and email it to the manufacturer's support team. They can tell you the screen size within a few hours.

Understanding the difference between screen size and screen resolution

Screen size (measured in inches) and screen resolution (measured in pixels) are two separate things. A 27-inch monitor might have a resolution of 1920 × 1080 pixels, while another 27-inch monitor might have 2560 × 1440 pixels. Both are 27 inches diagonally, but the second one packs more pixels into the same physical space, so text and images appear sharper.

Knowing your monitor size helps you understand how much desk space you need and how far away you should sit. Knowing your resolution helps you understand how sharp the image will be and whether your graphics card can handle it. You need both numbers to make sense of your monitor's capabilities, but only the diagonal measurement is what people mean when they say "monitor size."

Common monitor sizes and what they are used for

Most office and home monitors fall into a few standard sizes. A 21.5-inch or 24-inch monitor is typical for a single-monitor desk setup — it takes up a reasonable amount of space without dominating the desk. A 27-inch monitor is popular for people who want more screen real estate for spreadsheets, video editing, or gaming. A 32-inch monitor is large enough that some people use it as their only screen, though it can feel overwhelming if you sit close to it.

Ultrawide monitors, which are wider than they are tall, are measured the same way — diagonally corner to corner. A 34-inch ultrawide is wider than a standard 27-inch monitor but not as tall, so it takes up a different footprint on your desk.

Laptop screens are also measured diagonally, which is why a 15-inch laptop screen is smaller than a 24-inch desktop monitor even though the numbers seem close. The aspect ratio (the shape of the screen) is different, so the actual viewing area is much smaller on the laptop.

Why manufacturers use diagonal measurement instead of width or height

The diagonal measurement became the standard because it is a single number that captures the overall size of the screen regardless of its shape. A 16:9 widescreen monitor and a 4:3 square monitor could have the same diagonal but very different widths and heights. By using the diagonal, manufacturers created one universal way to compare screens.

This standard has been in place since the era of television, and it stuck because it is straightforward and consistent. Every monitor you buy will be labeled this way, so once you know your current monitor size, you can easily compare it to other options when you are shopping for a replacement.

Frequently Asked Questions

Does the bezel count toward monitor size?

No. The bezel is the plastic frame around the screen. Measure only the visible screen area, from the edge of the image to the opposite edge. The bezel does not count.

What if my monitor is curved?

Measure the same way — diagonally from corner to corner of the visible screen. The curve does not change the measurement. Curved monitors are labeled by their diagonal size just like flat ones.

Can I measure from the outside of the screen instead of the image area?

You can, but you will get a slightly larger number. Manufacturers measure the image area only, so measure from where the picture actually begins, not from the edge of the glass or plastic.

Is there a difference between screen size and viewing area?

Not in the way manufacturers label it. The diagonal measurement refers to the visible image area. Some older monitors had a small border of black space around the image, but modern monitors use the full screen for the image.

Why do some monitors list two different sizes?

This usually means the listing includes both the screen size and the stand size, or the screen size and the overall product dimensions. Always use the screen size (the diagonal measurement) when comparing monitors. Check the specifications section of the product page to confirm which number is the actual screen size.