Measure diagonally from corner to corner to find your monitor's true screen size

Monitor size is always measured diagonally—from the bottom-left corner to the top-right corner (or top-left to bottom-right). This diagonal measurement, given in inches, is what manufacturers list as the screen size. A 24-inch monitor means the distance from one corner to the opposite corner is 24 inches, not the width or height alone.

You will need a measuring tape or ruler long enough to span the diagonal. A cloth measuring tape works best because it bends around the curved edges of modern monitors, but a rigid ruler or straightedge will work if you measure carefully. Avoid measuring the plastic bezel (the frame around the screen)—measure only the visible screen area itself, from the edge where the image actually appears.

If you cannot measure physically, you can look up your monitor's model number in the manual or on the manufacturer's website. The screen size is always listed in the specifications. This is the fastest method if you have the documentation available.

Key Takeaways

  • Monitor size is the diagonal measurement from one corner of the screen to the opposite corner, measured in inches.
  • Measure only the visible screen area, not the plastic frame or bezel surrounding it.
  • A cloth measuring tape gives the most accurate result because it follows the screen's curve without gaps.
  • If you cannot measure, find your monitor's model number and look up the screen size in the product specifications online.
  • Common monitor sizes are 21.5, 24, 27, 32, and 34 inches, though sizes vary widely depending on the monitor type.

Gather the right measuring tools

A cloth measuring tape (the kind tailors use) is the ideal tool because it lies flat against the screen and bends smoothly around the edges without creating gaps. If you do not have one, a flexible ruler or even a piece of string works—measure the string afterward with a rigid ruler or measuring stick.

A rigid ruler or straightedge can work if you hold it diagonally across the screen and measure carefully, but it may not touch both corners evenly if your monitor has a curved screen. Avoid using your fingers or hand spans to estimate—these are too imprecise for an accurate measurement.

Make sure whatever you use is long enough. Most monitors under 32 inches fit within a standard 36-inch measuring tape. For larger monitors, you may need a longer tape or the string-and-ruler method.

Position your monitor and measure the diagonal

Turn on your monitor so you can see the screen edges clearly. Place one end of your measuring tape at the bottom-left corner where the screen image begins (not the plastic frame). Pull the tape diagonally across to the top-right corner. Keep the tape taut and as straight as possible along the diagonal path.

Read the measurement where the tape reaches the top-right corner. If you are using a string, mark where it ends at the top-right corner, then lay the string straight and measure it with a ruler. Round to the nearest half-inch—manufacturers do the same, so a measurement of 23.8 inches rounds to 24 inches.

Repeat the measurement from top-left to bottom-right as a check. Both diagonals should be the same length. If they differ by more than a quarter-inch, your monitor may have an unusual shape, or you may have measured slightly off-center. Measure once more, making sure the tape touches both corners squarely.

Understand what the measurement tells you

Your diagonal measurement is the screen size that manufacturers use to classify monitors. This number does not tell you the width or height individually—those depend on the monitor's aspect ratio (the proportion of width to height). A 24-inch monitor with a 16:9 aspect ratio (wider than it is tall) has different width and height than a 24-inch monitor with a 4:3 aspect ratio (closer to square).

The screen size also does not include the bezel. A 24-inch monitor's actual physical width and height are larger because of the plastic frame around the screen. If you need the exact width and height for a desk or mount, look up the full dimensions in the product manual—these are listed separately from screen size.

Knowing your screen size helps you understand monitor specifications you see online, compare monitors when shopping, and determine whether a monitor will fit your space or mounting hardware.

Find your monitor's size if you cannot measure

Look for a label or sticker on the back of your monitor. Manufacturers often print the model number there. Once you have the model number, search for it on the manufacturer's website (Dell, LG, ASUS, HP, and others all have searchable product databases). The screen size appears in the specifications section, usually listed as "Screen Size" or "Display Size."

If you have the original manual or packaging, the screen size is printed on the box and in the specifications page of the manual. You can also check your computer's display settings—on Windows, right-click the desktop and select "Display settings," then scroll down to "Advanced display settings." Some systems list the monitor model there, though not always the screen size.

As a last resort, you can contact the manufacturer's support team with your model number, and they will confirm the screen size. This takes longer but guarantees accuracy.

Common monitor sizes and what they mean

Most desktop monitors fall into a few standard sizes. 21.5 and 24 inches are the most common for everyday work and gaming. 27 inches is popular for content creation and detailed work because the larger screen reduces eye strain. 32 inches and larger are typically used for professional video editing, design, or as secondary displays in multi-monitor setups.

Ultrawide monitors (29, 34, or 38 inches) measure diagonally the same way but have an aspect ratio wider than standard 16:9, so they are much wider than they are tall. A 34-inch ultrawide is wider than a standard 27-inch monitor but shorter in height.

Laptop screens are measured the same way—a 15-inch laptop has a 15-inch diagonal screen—but are rarely larger than 17 inches. Tablet screens range from 7 to 13 inches diagonally. Knowing the standard sizes helps you understand what to expect when you see a monitor advertised.

Avoid common mistakes when measuring

Do not measure the plastic bezel or frame. The screen size refers only to the visible image area. If you include the frame, your measurement will be larger than the actual screen size and will not match the manufacturer's specification.

Do not measure straight across (width) or straight down (height). Monitors are always classified by diagonal measurement, never by width or height alone. Measuring width or height will give you a number that does not correspond to any standard monitor size.

Do not assume your monitor's size based on how it looks. Screen size and perceived size are different—a 27-inch monitor sitting far away may look smaller than a 24-inch monitor sitting close to you. Always measure or look up the specification to know for certain.

If your monitor has a curved screen, make sure your measuring tape or string follows the curve of the screen itself, not the air above it. A cloth tape will naturally conform to the curve; a rigid ruler may not.

Frequently Asked Questions

Does the bezel size affect the screen size measurement?

No. Screen size is the diagonal of the visible image area only. The plastic frame around the screen does not count. Two monitors with the same screen size may have different overall widths and heights if one has a thicker bezel, but their screen sizes are identical.

What if my monitor is curved or has rounded corners?

Measure from the corner where the image begins, following the curve of the screen with a flexible measuring tape. For rounded corners, measure to the point where the screen image ends, not to the outer edge of the plastic. A cloth tape works best for curved screens.

Can I measure a monitor that is mounted on an arm or wall?

Yes. You can measure a mounted monitor the same way—diagonally from corner to corner of the visible screen area. The mounting method does not change the screen size. Make sure the monitor is stable and level before you measure.

Why do manufacturers use diagonal measurement instead of width or height?

Diagonal measurement is a single number that works for all aspect ratios. A 24-inch monitor could be 16:9 (widescreen), 16:10, or 4:3 (more square), and each would have different width and height but the same diagonal. Diagonal gives manufacturers one standard way to classify all monitors.

Is the screen size the same as the resolution?

No. Screen size is the physical diagonal measurement in inches. Resolution is the number of pixels displayed (like 1920×1080 or 2560×1440). Two monitors can have the same screen size but different resolutions, or the same resolution but different screen sizes.