Measure diagonally from corner to corner with a tape measure

Monitor size is always the diagonal distance from one corner of the screen to the opposite corner, measured in inches. This is the only measurement that matters when you see a monitor listed as 24 inches, 27 inches, or 32 inches. You do not measure the width or height separately — the diagonal is the standard the entire industry uses.

To measure your own monitor, take a tape measure and place it at the bottom-left corner of the screen itself (not the frame or bezel). Pull it diagonally up to the top-right corner. Write down the number where the tape ends. If you get 24.5 inches, your monitor is a 24-inch model. If you get 27.2 inches, it is a 27-inch model. Rounding to the nearest whole number is normal — manufacturers do the same.

The measurement must be of the actual display area, not the plastic border around it. If you measure the outer edge of the bezel, you will get a larger number that does not match any real monitor size.

Key Takeaways

  • Monitor size is always measured diagonally from the bottom-left corner of the screen to the top-right corner, in inches.
  • Measure only the display itself, not the plastic frame or bezel surrounding it.
  • If you do not have a tape measure, you can find the exact size in your monitor's manual or on the manufacturer's website using the model number.
  • The diagonal measurement is the only size specification that matters — width and height vary by aspect ratio even on monitors of the same diagonal size.
  • Common monitor sizes are 21.5, 24, 27, 32, and 34 inches; your measurement should fall close to one of these numbers.

Find the model number if you cannot measure

If you do not have a tape measure or cannot reach the screen safely, the model number will tell you the exact size. Look on the back of the monitor for a sticker or label. The model number is usually printed there along with the manufacturer name. Write down the complete model number — it often looks like "Dell S2721DGF" or "LG 27GP850".

Go to the manufacturer's website and search for that model number in their support or product pages. The specifications section will list the screen size in inches. This method is faster and more precise than measuring by hand, and it also tells you other details like the resolution and refresh rate.

If the sticker is worn or unreadable, check the original box or manual if you still have it. The size is always printed on the packaging. You can also right-click on your desktop, select Display Settings (on Windows) or System Preferences (on Mac), and look for the monitor name — it often includes the size, though not always.

Understand why diagonal measurement matters

Monitors with the same diagonal size can have different widths and heights depending on their aspect ratio. A 27-inch monitor in standard 16:9 widescreen format is wider and shorter than a 27-inch monitor in 16:10 format. Both measure 27 inches corner to corner, but they look different on your desk. The diagonal is the only measurement that stays constant across all aspect ratios.

This is why manufacturers always advertise by diagonal size — it is the one number that is truly comparable between models. If you see a monitor listed as "27 inches," you know exactly how large the screen is, regardless of whether it is ultrawide, standard widescreen, or portrait-oriented.

Check the specifications if you are shopping for a replacement

When you are looking at monitors online or in a store, the size is always listed in the product title or specifications. Look for a number followed by "inch" or the double-quote symbol (″). A listing that says "27-inch 1440p monitor" or "27″ gaming display" is telling you the diagonal measurement.

Do not confuse monitor size with resolution. A 27-inch monitor can have 1080p, 1440p, or 4K resolution — the size and the sharpness are separate things. You need to check both the diagonal size and the resolution if you want to match your current setup or upgrade to something specific.

If you are replacing a monitor and want the same size, measure your current one and then search for monitors with that same diagonal measurement. This ensures the new monitor will fit your desk space and viewing distance the same way the old one did.

Account for the bezel when planning desk space

The diagonal measurement tells you the screen size, but it does not tell you how much space the monitor will take up on your desk. The plastic frame around the screen, called the bezel, adds extra width and height. A 27-inch monitor might have a screen that is roughly 24 inches wide, but with the bezel it could be 26 inches wide overall.

If you are buying a new monitor and need to know whether it will fit your desk, measure the width and height of the entire monitor housing, not just the screen. This number is also listed in the full specifications on the manufacturer's website. Check the dimensions section, which usually shows width, height, and depth in inches or centimeters.

Common monitor sizes and what they mean

Most desktop monitors fall into a few standard sizes. A 21.5-inch or 24-inch monitor is typical for office work and general use. A 27-inch monitor is popular for gaming and content creation because it offers more screen space without being too large. A 32-inch monitor is used for professional work like video editing or design, or for immersive gaming setups. Ultrawide monitors come in 34-inch and 38-inch sizes and are much wider than they are tall.

If your measurement falls between two standard sizes — for example, you measure 25.8 inches — your monitor is likely a 24-inch model that is slightly larger than the nominal size due to manufacturing tolerance. Manufacturers allow small variations, and a measurement within half an inch of a standard size means you have found your monitor's true category.

Frequently Asked Questions

Should I measure the screen or the entire monitor including the stand?

Measure only the screen itself, from corner to corner of the display area. Do not include the stand, the base, or the plastic bezel. The monitor size refers only to the diagonal of the viewable screen, not the physical footprint of the entire device.

What if my measurement does not match any standard size?

If you measure 23.5 inches or 26.8 inches, you likely have a monitor that is close to a standard size but slightly off due to manufacturing variation or rounding. Check the model number on the back to confirm the exact size from the manufacturer. The model number is always more accurate than a hand measurement.

Does monitor size affect how sharp the image looks?

No. Sharpness depends on resolution (like 1080p or 1440p) and pixel density, not on the diagonal size. A 24-inch 1440p monitor can look sharper than a 27-inch 1440p monitor because the pixels are packed more densely. Always check both the size and the resolution when comparing monitors.

Can I use my phone to measure instead of a tape measure?

A smartphone with a measuring app can work, but a physical tape measure is more reliable. If you use a phone app, place it flat against the screen and measure from the exact corner of the display, not the bezel. The app's accuracy depends on your phone's sensors and how steadily you hold it.

Is the monitor size the same as the screen resolution?

No. Size is the diagonal measurement in inches. Resolution is the number of pixels displayed, like 1920×1080 or 2560×1440. A 27-inch monitor can have any resolution. You need to check both specifications separately when shopping or comparing monitors.