Measure diagonally from corner to corner

Monitor size is always the diagonal distance across the screen, measured in inches from one corner to the opposite corner. This is the only measurement that matters when you see a monitor listed as 24 inches, 27 inches, or 32 inches. The width and height vary depending on the aspect ratio — a 27-inch ultrawide looks different from a 27-inch standard monitor — but the diagonal is always what the label refers to.

To measure your own monitor, use a tape measure or ruler and place it at the bottom-left corner of the screen. Pull it diagonally up to the top-right corner, keeping it flat against the glass or bezel. Write down the number where it ends. That measurement, in inches, is your screen size.

Do not measure the frame or plastic bezel around the screen. Measure only the visible display area — the part that actually shows the image. If you measure the outer casing, you will get a number that is larger than the true screen size.

Key Takeaways

  • Monitor size is always measured diagonally from corner to corner in inches, not by width or height.
  • Measure only the visible screen area, not the plastic frame or bezel surrounding it.
  • If you cannot physically measure, check your monitor's manual, the manufacturer's website, or the Windows or Mac system settings, which often list the screen size.
  • Aspect ratio (the width-to-height proportion) changes how a monitor looks at the same diagonal size, so two 27-inch monitors may have different widths.
  • The diagonal measurement is the only standard used by manufacturers, so it is the only number you need to compare monitors.

Find your screen size in system settings

If you do not have a tape measure or prefer not to measure, your operating system usually knows your monitor's size. On Windows, right-click the desktop, select Display settings, scroll down, and look for a section labeled Scale and layout or Advanced display settings. Some versions of Windows list the screen size here, though not all do.

On Mac, click the Apple menu, select System Settings (or System Preferences on older versions), then go to Displays. The resolution and sometimes the screen size appear in the main panel. If the size is not listed, you may need to check the monitor's manual or the manufacturer's website instead.

This method works best if you bought the monitor recently and the system detected it correctly. Older monitors or those connected through adapters may not report their size accurately in settings.

Check the monitor's manual or label

The quickest way to find your screen size is to look at the documentation that came with the monitor. The manual, the original box, or a sticker on the back of the monitor itself usually lists the screen size prominently. Search for words like "screen size," "display size," or "diagonal" in the manual's specifications section.

If you no longer have the manual, look for a model number on the monitor's bezel or back panel. Type that model number into a search engine along with the word "specifications" or "specs." The manufacturer's website will show you the exact screen size and other details like resolution and refresh rate.

The model number is usually a combination of letters and numbers — for example, "Dell S2721DGF" or "LG 27UP550." This number is your fastest route to accurate information.

Understand aspect ratio and why it matters

Two monitors with the same diagonal size can look very different because of aspect ratio — the relationship between width and height. A standard monitor is 16:9 (wider than it is tall), while an ultrawide is 21:9 or 32:9 (much wider). A 27-inch 16:9 monitor is roughly 24 inches wide and 13 inches tall, but a 27-inch ultrawide is about 32 inches wide and 9 inches tall.

When you measure diagonally, you get the same number, but the shape is completely different. This matters if you are replacing a monitor and want to know whether the new one will fit in your desk space. Measure the width and height separately if you need to confirm it will fit your setup, but remember that the diagonal is the only number manufacturers use to label and compare monitors.

Use an online calculator if you know the resolution

If you know your monitor's resolution (the number of pixels across and down) and aspect ratio, you can calculate the diagonal size using an online calculator. Search for "monitor size calculator" and enter your resolution. The calculator will show you the approximate screen size.

This method is less accurate than measuring or checking the manual because it assumes a standard pixel density, which varies by monitor. A 1920 × 1080 resolution could be on a 24-inch monitor or a 27-inch monitor depending on how densely the pixels are packed. Use this method only as a rough check, not as your primary way to find the size.

Measure width and height if you need desk space information

The diagonal tells you the screen size, but it does not tell you whether the monitor will fit on your desk. Measure the width (left edge to right edge) and height (top to bottom) of the monitor's bezel if you need to know the physical space it takes up. Write both numbers down and compare them to your available desk space.

Some monitors come with adjustable stands that change the height, so measure with the stand at the height you plan to use it. If you are mounting the monitor on an arm or wall bracket, you only need to know the width and depth (how far it sticks out from the wall), not the height.

Frequently Asked Questions

Is the monitor size the same as the screen resolution?

No. Screen size is the diagonal measurement in inches. Resolution is the number of pixels — for example, 1920 × 1080. Two monitors with the same size can have different resolutions, and two monitors with the same resolution can have different sizes. They measure different things.

Why do manufacturers measure diagonally instead of by width?

The diagonal is the only measurement that stays the same across different aspect ratios. A 27-inch 16:9 monitor and a 27-inch ultrawide have different widths but the same diagonal. Using the diagonal lets manufacturers compare monitors fairly regardless of shape.

Can I measure in centimeters instead of inches?

Yes, but monitor sizes are always sold and labeled in inches. If you measure in centimeters, divide by 2.54 to convert to inches. A monitor that measures 68 centimeters diagonally is roughly 27 inches.

What if my monitor is curved or has an unusual shape?

Measure the diagonal of the visible screen area the same way you would for a flat monitor. The curve does not change the diagonal measurement — only the physical depth of the monitor changes. Curved monitors are still labeled by their diagonal screen size.

Does the bezel thickness affect the screen size measurement?

No. The bezel is the plastic or metal frame around the screen. Measure only the glass or display area itself, not the frame. A monitor with a thick bezel and one with a thin bezel can be the same screen size if their display areas are the same diagonal.