Measure the diagonal distance across your screen to find its true size
Monitor size is always measured diagonally from one corner to the opposite corner, not by width or height alone. This is the number you see in product listings — a "24-inch monitor" means the diagonal distance is 24 inches. To measure your own monitor, you need a measuring tape, a straight edge, and about two minutes.
The diagonal measurement matters because it's the standard way manufacturers describe screens, and it's what you'll need to know if you're replacing a monitor or comparing different models. It also helps you understand the actual screen area you're working with, since two monitors with the same diagonal can have different widths and heights depending on their aspect ratio.
Key Takeaways
- Monitor size is always the diagonal measurement from corner to corner, measured in inches.
- Measure from the inside edge of the bezel (the plastic frame), not the outer edge of the monitor casing.
- A 24-inch monitor with a 16:9 aspect ratio is roughly 21 inches wide and 12 inches tall.
- If you can't measure physically, you can find your monitor's model number and look up the specs online.
What you need to measure accurately
Gather a fabric measuring tape (the kind tailors use) or a metal tape measure. A ruler works if your monitor is small, but a tape measure is easier for larger screens. You'll also want a straight edge — a ruler or the edge of a piece of paper — to help you line up the measurement from corner to corner.
Turn off your monitor before you measure. This makes it safer to handle and easier to see the actual screen edges without glare. You don't need to unplug it; just power it down.
How to measure from corner to corner
Place your measuring tape at the inside corner of the screen — where the actual display area begins, not where the plastic frame starts. The bezel (the border around the screen) doesn't count toward the measurement. Start at the bottom-left inside corner and stretch the tape diagonally up to the top-right inside corner.
Keep the tape taut but not pulled so hard that it bends. If you're using a fabric tape, it should lie flat against the screen surface. Read the number where the tape reaches the opposite corner. Round to the nearest half-inch if the measurement falls between numbers — a monitor that measures 23.6 inches is sold as a 24-inch monitor.
If your monitor is curved, run the tape along the curve from corner to corner rather than trying to stretch it in a straight line through the air. The measurement should still follow the diagonal path across the visible screen area.
Understanding aspect ratio and what it means for screen dimensions
A monitor's aspect ratio is the relationship between its width and height. The most common ratio today is 16:9 (widescreen), but you'll also see 16:10, 21:9 (ultrawide), and 4:3 (older monitors). The aspect ratio doesn't change the diagonal measurement, but it does change how wide or tall the screen actually is.
A 24-inch monitor with 16:9 aspect ratio is approximately 21 inches wide and 12 inches tall. The same 24-inch diagonal with a 16:10 ratio would be about 20.9 inches wide and 13 inches tall — slightly taller and less wide. If you need the exact width and height for your desk space, you can calculate them using the diagonal and aspect ratio, or look up your monitor's model number to find the full specifications.
Finding your monitor size if you can't measure it
If your monitor is mounted on a wall, in an awkward position, or you straightforward prefer not to measure, you can find the size another way. Look for a sticker or label on the back of the monitor that lists the model number. Search that model number online — most manufacturers' websites and retailer product pages list the diagonal screen size in the specifications.
You can also check your computer's display settings. On Windows, right-click the desktop, select "Display settings," scroll down, and look for "Display information" — though this method doesn't always show the physical screen size. On Mac, go to System Preferences > Displays and click "Scaled" to see resolution options, but you may still need to look up the model number for the actual diagonal measurement.
Common monitor sizes and their approximate dimensions
| Diagonal Size | 16:9 Width × Height | 16:10 Width × Height | Common Use |
|---|---|---|---|
| 21.5 inches | 19" × 10.7" | 18.8" × 11.8" | Budget office work |
| 24 inches | 21" × 12" | 20.9" × 13" | Standard office and gaming |
| 27 inches | 23.5" × 13.2" | 23.5" × 14.7" | Photo and video work |
| 32 inches | 27.9" × 15.7" | 27.9" × 17.5" | Large workspace or 4K |
| 34 inches | 29.8" × 12.5" | N/A | Ultrawide (21:9 ratio) |
These dimensions are approximate because bezels vary slightly between manufacturers. The actual visible screen area may be slightly smaller than these numbers suggest. Use this table as a guide for how much desk space a monitor will need, not as an exact specification.
Why diagonal measurement matters for your setup
Knowing your monitor's diagonal size helps you understand how much screen real estate you actually have. Two monitors with the same diagonal but different aspect ratios will feel different — a 27-inch ultrawide (21:9) gives you more horizontal space than a 27-inch standard (16:9), even though the diagonal is the same.
The diagonal measurement also matters when you're shopping for a replacement or adding a second monitor. If you want a monitor that feels similar in size to your current one, matching the diagonal is the quickest way to get close. If you want more screen area without changing the diagonal, you'd need to switch to a different aspect ratio — for example, moving from 16:9 to 16:10 gives you more vertical space.
Frequently Asked Questions
Do I measure the bezel or just the screen itself?
Measure only the screen itself — the part that actually displays the image. Start at the inside edge of the bezel (the plastic or metal frame around the screen) and measure to the opposite inside corner. The bezel thickness doesn't count toward the monitor size.
What if my measurement doesn't match a standard size?
Monitor sizes are sold in standard increments (21.5, 24, 27, 32 inches), but your measurement might land between them or be slightly off due to rounding or bezel variation. If you measure 23.6 inches, that's a 24-inch monitor. If you measure 26.8 inches, that's a 27-inch monitor. Manufacturers round to the nearest standard size.
Does the stand or mounting arm affect the monitor size?
No. The monitor size is only the diagonal of the screen itself. The stand, arm, or wall mount doesn't change the measurement. If you're measuring a monitor that's mounted on an arm, you can still measure the screen diagonal the same way.
Can I use my phone's camera to measure instead of a tape measure?
Some phone apps claim to measure distances using the camera, but they're not reliable for monitor screens because the angle and distance from the camera affect accuracy. A physical tape measure is faster and more accurate. If you absolutely can't measure, looking up your monitor's model number online is a better option than using a camera app.
Why do manufacturers use diagonal instead of width or height?
The diagonal measurement is a single number that describes the overall size regardless of aspect ratio. Two monitors with different widths and heights can have the same diagonal, so it's a standardized way to compare screens. It's also the measurement that feels most natural to consumers — it describes how "big" the screen is overall.