Measure diagonally from corner to corner
Monitor size is always the diagonal distance across the screen, measured 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. You measure from the bottom-left corner to the top-right corner (or top-left to bottom-right — either way gives the same result).
Use a measuring tape or ruler. Place one end at the corner of the screen itself, not the bezel or frame around it. Stretch the tape to the opposite corner and read the number where it lands. If you get 23.6 inches, that monitor is sold as a 24-inch display. If you get 26.9 inches, it is a 27-inch. Manufacturers round to the nearest whole number.
Do not measure the width or height alone — those numbers are not what the size refers to. A 24-inch monitor might be 21 inches wide and 12 inches tall, but the diagonal is what the industry calls the size.
Key Takeaways
- Monitor size is always measured diagonally from one corner of the screen to the opposite corner, not the width or height.
- Measure from the actual screen surface, not the plastic frame or bezel around it.
- The measurement you get will be slightly less than the advertised size because manufacturers round down — a 24-inch monitor typically measures 23.6 inches.
- You can also find the exact screen size in the monitor's manual or specifications sheet without measuring at all.
Why manufacturers round the diagonal
A 24-inch monitor does not actually measure exactly 24 inches. The true diagonal is usually 23.6 or 23.8 inches, but the industry rounds to the nearest whole number for marketing. This is standard across all monitor makers — Dell, LG, ASUS, BenQ, and others all follow the same practice.
The rounding exists because the exact diagonal depends on the aspect ratio (the width-to-height proportion). A 24-inch monitor with a 16:9 aspect ratio will have a slightly different diagonal than a 24-inch monitor with a 16:10 aspect ratio, even though both are called 24-inch displays. Manufacturers use the rounded number as the size category rather than listing the exact measurement.
Find the size without measuring
If you do not have a measuring tape or prefer not to measure, check the monitor's manual or the specifications sheet. The exact diagonal measurement is always listed there. You can also look up the model number on the manufacturer's website — search "[brand name] [model number] specifications" and the screen size will appear in the first result.
The model number is usually printed on the back of the monitor or on a sticker underneath. It often contains the size as part of the name — a Dell S2422HZ, for example, is a 24-inch monitor. LG model numbers work the same way: an LG 27UP550 is 27 inches.
Aspect ratio affects how the screen looks, not the size
Two monitors can both be 27 inches but look different because of aspect ratio. A 27-inch monitor with 16:9 aspect ratio (the most common) is wider and shorter. A 27-inch monitor with 16:10 aspect ratio is slightly taller and less wide. Both measure 27 inches diagonally, but the shape of the screen is different.
Ultrawide monitors complicate this further. A 34-inch ultrawide monitor might be 21:9 aspect ratio, making it much wider than a standard 34-inch monitor would be. The diagonal measurement is still 34 inches, but the screen stretches much farther left and right. When shopping for a monitor, check both the size and the aspect ratio to understand what the screen will actually look like on your desk.
What to do if the screen is curved
Curved monitors are measured the same way — diagonally from corner to corner. The curve does not change how the size is calculated. A 32-inch curved monitor has the same 32-inch diagonal as a flat 32-inch monitor, even though the curved one wraps around slightly.
Measure along the surface of the screen itself, following the curve if there is one. The tape will naturally follow the contour. The result should match the advertised size within a tenth of an inch.
Common monitor sizes and their actual measurements
| Advertised Size | Typical Actual Diagonal | Common Aspect Ratio |
|---|---|---|
| 21.5 inches | 21.4 to 21.5 inches | 16:9 |
| 24 inches | 23.6 to 23.8 inches | 16:9 or 16:10 |
| 27 inches | 26.9 to 27.0 inches | 16:9 or 16:10 |
| 32 inches | 31.5 to 32.0 inches | 16:9 |
| 34 inches | 33.8 to 34.0 inches | 21:9 (ultrawide) |
These ranges account for different manufacturers and aspect ratios. Your actual measurement may fall anywhere within the range and still be correct for that size category.
Frequently Asked Questions
Should I measure the bezel or just the screen?
Measure only the screen itself, not the plastic or metal frame around it. The bezel does not count toward the monitor size. Place your measuring tape at the edge of the actual display area where the image appears, not where the frame begins.
Does the stand or base affect the measurement?
No. The stand and base are not part of the size calculation. Measure only the screen from corner to corner. The height of the stand or the width of the base does not matter.
What if my measurement is 0.5 inches less than the advertised size?
That is normal. Manufacturers round the diagonal to the nearest whole number, so a monitor advertised as 24 inches typically measures between 23.5 and 23.8 inches. Your measurement is correct.
Can I measure in centimeters instead of inches?
Yes. Measure diagonally the same way, and you will get the result in centimeters. A 24-inch monitor measures approximately 60 centimeters diagonally. Convert by multiplying inches by 2.54 if you need to compare measurements.
Why does my monitor look smaller than the advertised size?
The diagonal measurement can feel smaller than expected because it does not tell you the full width or height. A 27-inch monitor with 16:9 aspect ratio is about 24 inches wide and 13.5 inches tall. If you are used to a wider or taller screen, the 27-inch might feel compact even though the diagonal is substantial.