Measure your screen diagonally from corner to corner

The size of a PC monitor is always measured diagonally—from the bottom-left corner to the top-right corner, or vice versa. 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 measure only the visible screen area, not the plastic bezel or frame around it. If you're measuring an existing monitor, use a soft measuring tape or a ruler. If you're shopping for a replacement and don't have the original specs, this diagonal measurement is the fastest way to find out what you have.

Key Takeaways

  • Monitor size is always the diagonal measurement in inches, from corner to corner of the visible screen.
  • Measure only the display itself, not the plastic frame or bezel surrounding it.
  • Use a soft measuring tape for accuracy, and measure from the inner edge of the screen to avoid including the frame.
  • If you can't measure physically, check the monitor's back panel, manual, or the manufacturer's website using the model number.
  • Common PC monitor sizes are 21.5, 24, 27, 32, and 34 inches, though sizes vary by model and brand.

What you need to measure accurately

A soft measuring tape (the kind tailors use) works best because it won't damage the screen and bends easily around the corners. A rigid ruler or metal tape measure can work too, but be gentle—don't press hard against the screen surface. If you don't have a measuring tape, a piece of string or yarn and a ruler will do: lay the string diagonally across the screen, mark where it reaches each corner, then measure the string against a ruler.

Make sure the monitor is powered on or at least visible so you can see exactly where the screen edges are. The bezel (the plastic frame) can be thick or thin depending on the monitor model, so you need to see the actual display boundary to measure correctly.

Step-by-step measuring process

Start at the bottom-left corner of the visible screen—the point where the display itself begins, not where the plastic frame starts. Place the end of your measuring tape or ruler at that inner corner. Stretch it diagonally across to the top-right corner of the screen, again measuring only the display area, not the bezel.

Read the measurement where the tape or ruler reaches the top-right corner. If the number falls between two marks (for example, between 23 and 24 inches), round to the nearest half-inch. Most monitors are sold in standard sizes, so your measurement should be close to a common size like 21.5, 24, 27, 32, or 34 inches. If your measurement is 23.8 inches, the monitor is likely a 24-inch model.

Repeat the measurement from the top-left to the bottom-right corner 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 aspect ratio, but the average of the two measurements will still give you the correct size.

Finding the size without measuring

If measuring is inconvenient, look at the back or bottom of the monitor for a label or sticker with the model number. Manufacturers usually print this information on a white or silver label. Once you have the model number, search for it on the manufacturer's website (Dell, LG, ASUS, HP, BenQ, and others all have searchable product databases) or type the model number into a search engine. The product page will list the screen size in the specifications.

You can also check the monitor's original box or manual if you still have them. The size is always printed on the front of the box and in the manual's specifications section. If you bought the monitor used or inherited it, the seller or previous owner may have the documentation.

Understanding aspect ratio and how it differs from size

Screen size (the diagonal measurement) is different from aspect ratio, which describes the shape of the screen. Most PC monitors have a 16:9 aspect ratio (wider than it is tall), while some professional or older monitors use 4:3 (more square-shaped). A few specialized monitors are 21:9 (ultrawide). Two monitors can be the same diagonal size but have different widths and heights depending on their aspect ratio.

When you measure diagonally, you're getting the overall size, but the aspect ratio tells you the proportions. If you need to know both—for example, to fit a monitor into a specific desk space—you would measure the width and height separately after finding the diagonal. But for identifying what size monitor you have, the diagonal measurement alone is what matters.

Common monitor sizes and what they look like

Most desktop PC monitors fall into a few standard sizes. A 24-inch monitor is the most common for general use and office work—it's large enough to see detail without taking up too much desk space. A 27-inch monitor is popular for gaming and creative work because it offers more screen real estate. Smaller monitors like 21.5 inches are less common now but still exist in budget or secondary setups. Larger monitors like 32 or 34 inches are used by professionals who need to see a lot of information at once, such as video editors or financial analysts.

If your measurement doesn't match a standard size exactly, it's likely because you measured the bezel slightly or the monitor has an unusual dimension. Rounding to the nearest standard size will tell you what you have. For example, a measurement of 23.6 inches is a 24-inch monitor; 26.9 inches is a 27-inch monitor.

Frequently Asked Questions

Do I measure the screen with the bezel included?

No. Measure only the visible display area, from the inner edge of the screen to the inner edge on the opposite corner. The plastic frame around the screen does not count toward the size.

What if my monitor is curved or has rounded corners?

Measure from the innermost point of the display at each corner. For a curved screen, imagine a straight line from corner to corner and measure that distance. The curvature does not change the diagonal measurement.

Can I measure width and height instead of diagonally?

You can, but it's not how monitor size is defined. Manufacturers always list the diagonal. If you measure width and height, you would need to use the Pythagorean theorem (width² + height² = diagonal²) to convert to the standard size. Measuring diagonally is simpler and gives you the number directly.

What if I measure and get a size that doesn't match any standard monitor?

Check that you measured from the inner edge of the display, not the bezel. If you did, your monitor may be an older or specialty model. Search the model number online to confirm the actual size, or round your measurement to the nearest standard size (21.5, 24, 27, 32, or 34 inches).

Does screen size affect how sharp the image looks?

Size alone does not determine sharpness. Sharpness depends on resolution (the number of pixels) and pixel density (pixels per inch). A 24-inch monitor with 1920×1080 resolution and a 27-inch monitor with the same resolution will have different pixel densities because the pixels are spread over a larger area on the 27-inch screen.