Measure Your Monitor Diagonally, Corner to Corner
Monitor size is always measured diagonally across the screen, from one corner to the opposite corner. This is the number you see advertised—a "24-inch monitor" means the distance from the bottom-left corner to the top-right corner is 24 inches. You measure only the visible screen area, not the plastic bezel or frame around it.
Use a measuring tape or ruler and place it at the bottom-left corner of the screen itself (where the image actually displays). Pull it straight across to the top-right corner and read the measurement in inches. If you measure in centimeters, divide by 2.54 to convert to inches. Write down the number—this is your monitor's diagonal measurement.
The reason manufacturers use diagonal measurement is historical: it's the longest single line across a rectangle, so it sounds larger than width or height alone. A 27-inch monitor might be only 24 inches wide, but the diagonal is what gets advertised and what you'll see on the box or spec sheet.
Key Takeaways
- Monitor size is the diagonal measurement from bottom-left to top-right corner of the visible screen, measured in inches.
- Measure only the screen itself, not the plastic frame or bezel around it.
- You will need a measuring tape or ruler and should measure in a straight line without bending or angling the tape.
- The width and height of a monitor vary depending on its aspect ratio, so diagonal is the only standard measurement all monitors share.
- If you cannot physically measure, you can find the exact diagonal in your monitor's manual or on the manufacturer's website by searching the model number.
Measure the Width and Height If You Need Them
Sometimes you need to know how much desk space a monitor will take up, or whether it will fit in a specific spot. For that, measure the width (left edge to right edge) and height (bottom to top) of the screen itself, not including the stand or base. Again, measure only the visible display area.
Width and height vary widely depending on the monitor's aspect ratio. A 24-inch monitor with a standard 16:9 ratio (widescreen) will be roughly 21 inches wide and 12 inches tall. A 24-inch monitor with a 16:10 ratio will be slightly taller. An ultrawide 34-inch monitor might be 32 inches wide but only 13 inches tall. The diagonal stays the same across different aspect ratios, but width and height do not.
If you are trying to fit a monitor into a shelf or cabinet, measure the width and height of that space first, then compare it to the monitor's dimensions. The manufacturer's spec sheet will list width and height in inches or millimeters—you do not have to measure yourself if you have the model number.
Find Your Monitor's Measurements Without Measuring
If you cannot reach the screen with a measuring tape, or if you want to verify your measurement, look up the monitor's model number. You will usually find it on a sticker on the back of the monitor or on the base. It might look like "Dell U2720Q" or "LG 27UP550".
Search that model number on the manufacturer's website (Dell, LG, ASUS, HP, BenQ, or whoever made it). The product page will have a "Specifications" or "Tech Specs" section listing the diagonal size, width, height, and depth. You can also find this information in the manual that came with the monitor, usually in the first few pages.
This method is faster and more accurate than measuring by hand, especially if the monitor is mounted on a wall or arm where it is hard to reach. The spec sheet will also tell you the screen resolution (like 1920×1080 or 3840×2160), which is useful if you are comparing monitors or troubleshooting display problems.
Understand the Difference Between Screen Size and Usable Space
The diagonal measurement tells you the monitor's size, but it does not tell you how much space is actually available for your work or games. That depends on the resolution—how many pixels fit on the screen. A 27-inch monitor with 1920×1080 resolution will feel cramped because the pixels are large. The same 27-inch monitor with 2560×1440 resolution will feel roomier because more pixels fit in the same physical space.
Resolution is separate from size. You cannot tell a monitor's resolution just by measuring it. A 24-inch monitor might have 1920×1080 pixels or 2560×1440 pixels—both are real products. The resolution is listed in the specs, not on the monitor itself. If you are choosing a new monitor, check both the diagonal size and the resolution to understand how much screen real estate you will actually have.
Pixel density (pixels per inch, or PPI) is another way to think about this. A 27-inch 1440p monitor has about 109 PPI. A 27-inch 4K monitor has about 163 PPI. Higher PPI means sharper text and images, but it also means smaller icons and windows unless you scale them up in your operating system.
Measure the Stand and Depth If Space Is Tight
The diagonal measurement and width/height tell you the size of the screen, but not how much room the monitor takes up on your desk. For that, you also need the depth—the distance from the front of the screen to the back of the stand. Measure from the front of the bezel straight back to the farthest point of the base or stand.
Monitor stands vary widely. A straightforward stand might add 6 to 8 inches of depth. A monitor arm or wall mount adds almost no depth. If you are working with a small desk or shelf, measure the depth of that space and compare it to the monitor's depth in the specs. A monitor that is 24 inches wide but 8 inches deep might not fit in a space that is 24 inches deep if there is a wall or other equipment behind it.
The spec sheet will list depth (sometimes called "D" or "Depth"). If you are replacing an old monitor, you can also measure your current setup to see how much space you have, then look for a new monitor that fits those dimensions.
Check the Bezel Width If You Are Using Multiple Monitors
The bezel is the plastic frame around the screen. If you are setting up two or more monitors side by side, a thicker bezel creates a visible gap between the images on each screen. Measure the bezel width by measuring from the edge of the visible screen to the outer edge of the plastic frame. Do this on the sides where the monitors will be next to each other.
Modern monitors usually have bezels between 0.2 and 0.5 inches wide. Some gaming or professional monitors have thinner bezels (0.1 to 0.2 inches). The thinner the bezel, the less noticeable the gap when you line up two monitors. If you are planning a multi-monitor setup, look for monitors with narrow bezels and check the spec sheet for the exact bezel width before you buy.
The bezel width is listed in the specifications as "Bezel Width" or sometimes "Frame Width." You do not need to measure it yourself unless you want to verify the spec sheet or compare two monitors side by side.
Frequently Asked Questions
Do I measure the screen or the whole monitor including the frame?
Measure only the visible screen area, not the plastic bezel or frame. The diagonal measurement goes from the corner where the image starts to the opposite corner where the image ends. The frame does not count toward the size.
What if my monitor is curved or has rounded corners?
Measure from the corner of the visible screen area, even if the corners appear slightly rounded on the outside. The spec sheet will list the diagonal as if the screen were a perfect rectangle. If you are measuring a curved monitor, place the tape measure along the curve of the screen itself, not around the outside edge of the bezel.
Can I measure in centimeters instead of inches?
Yes. Measure in centimeters, then divide by 2.54 to convert to inches. Monitor sizes are always advertised in inches, so converting makes it easier to match your measurement to the product listing. For example, 61 centimeters ÷ 2.54 = 24 inches.
Why do monitors use diagonal measurement instead of width?
The diagonal is the longest line across a rectangle, so it produces a larger number and sounds more impressive. It is also the only measurement that stays consistent across different aspect ratios. A 24-inch monitor could be 16:9, 16:10, or 21:9—the width and height change, but the diagonal stays 24 inches.
Where do I find the model number if I want to look up the specs?
Look on the back of the monitor or on the bottom of the base for a sticker with the model number. It usually includes the brand name (Dell, LG, ASUS) and a code like "U2720Q" or "27UP550." Search that code on the manufacturer's website to find the full specifications.