How to Measure Your Monitor Size: A Simple Step-by-Step Guide

Ever wondered how big your monitor actually is? You might see 15.6 inches, 24 inches, or 27 inches in a product listing, but those numbers don't tell you how wide the screen is or how much desk space it will take up.

That's because monitor size is measured differently from what you might expect. The advertised size usually refers to the diagonal distance across the visible screen, not its width or height.

Whether you're checking if a monitor will fit on your desk, comparing different displays, or shopping for a replacement, knowing how to measure it can save you some guesswork. You can do it with a measuring tape, a ruler, or even a simple calculation if you already know the screen's width and height.

Let's walk through the different methods and a few things worth watching out for along the way.

What Does Monitor Size Actually Mean?

Before grabbing a ruler, it's worth clearing up one thing: monitor size doesn't refer to the entire physical dimensions of the device. Manufacturers use the diagonal measurement of the active display area to describe screen size.

There are actually three measurements you may come across when looking at monitor specifications.

Screen Size: The Diagonal Measurement

When a monitor is advertised as 15.6 inches or 27 inches, the number refers to the distance from one corner of the visible screen to the opposite corner.

For example, a 15.6-inch monitor has a diagonal screen measurement of approximately 15.6 inches. The bezel, or frame around the display, isn't included. Neither are the stand or outer casing.

You'll usually see monitor screen sizes listed in inches, even if the product's other dimensions are given in centimeters or millimeters.

Screen Width and Height

Width and height tell you how much horizontal and vertical space the active display takes up. These measurements depend on the screen's diagonal size and aspect ratio.

Here are three common aspect ratios you'll find on monitors:

• 16:9: A popular widescreen format for everyday computing, entertainment, and gaming.
• 16:10: Offers a little more vertical space, which can be useful for productivity and multitasking.
• 3:2: Has a taller screen shape that works well for reading, document editing, and other vertical tasks.

Here's something worth remembering: two monitors can have the same diagonal size but look quite different because their aspect ratios aren't the same.

Aspect ratio and screen size can also affect how far away you should sit from your display. You can learn more in our guide on how far away you should sit from a monitor.

Overall Monitor Dimensions

If you're trying to figure out whether a monitor will fit on your desk or inside a laptop bag, the diagonal measurement won't tell you everything.

That's where overall monitor dimensions come in. These usually describe the full width, height, and depth of the device, including its bezel and housing.

For example, a monitor listed as 545 × 327 × 12 mm has physical dimensions of 545 mm wide, 327 mm high, and 12 mm deep. Depending on the manufacturer, the listed height may or may not include the stand.

So, if you're planning a desk setup, checking a carrying case, or choosing a mounting system, make sure you look at the overall dimensions rather than relying on the advertised screen size alone.

How to Measure Your Monitor Size Manually

The easiest way to find out how big your monitor is? Measure the screen diagonally. You don't need any special equipment, just a ruler or measuring tape.

Get Your Measuring Tool Ready

A flexible measuring tape is usually the easiest option, but a standard ruler works too if it's long enough.

Before you start, decide whether you'll measure in centimeters or inches. If your measuring tool uses centimeters, that's perfectly fine. You can convert the result into inches afterward.

Measure From One Corner to the Other

Now it's time to measure. Follow these simple steps:

1. Identify the four corners of the active display area.
2. Place the starting point of your ruler or measuring tape at one corner of the visible screen.
3. Extend it diagonally to the opposite corner.
4. Read the measurement, making sure not to include the bezel.

You can measure from the top-left corner to the bottom-right corner, or from the top-right corner to the bottom-left. Either direction should give you approximately the same result.

One small detail: keep the measuring tool in a straight line between the two corners. Don't follow the outer frame or the curved surface of the monitor. Even with a curved display, the standard screen-size measurement is the straight-line distance between opposite corners.

Convert Centimeters to Inches

If your measurement is in centimeters, converting it to inches is pretty straightforward. Just divide the number by 2.54.

The formula:

Inches = Centimeters ÷ 2.54

For example, let's say your monitor measures 54.6 cm diagonally.

54.6 ÷ 2.54 ≈ 21.5 inches

That means you're looking at a monitor with an approximate screen size of 21.5 inches.

Quick Tip: Use Your Phone's Calculator

There's no need to work this out in your head. Just open the calculator app on your phone, enter the measurement in centimeters, and divide by 2.54.

• iPhone: The built-in Calculator app supports standard arithmetic. On supported iOS versions, you can also use its unit conversion feature to switch between centimeters and inches.
• Samsung Galaxy: Open the Calculator app and use the division function. Some models also include a unit conversion feature.

The exact layout and available features depend on your phone model and software version.

How to Calculate Monitor Size Without Measuring Diagonally

What if you don't have a measuring tape long enough to reach across the screen? Or maybe you already know the monitor's width and height from its product specifications.

Good news: you can still work out the diagonal size without measuring it directly. All you need is a little help from the Pythagorean theorem.

The Monitor Size Formula

The formula is:

D = √(W² + H²)

Where:

• D = Screen diagonal
• W = Screen width
• H = Screen height

In other words, square the width and height, add the two results together, and then find the square root.

Just make sure both measurements use the same unit. If your width and height are in centimeters, the diagonal will also be in centimeters.

A Step-by-Step Example

Let's say you have a monitor with the following active display dimensions:

• Width: 47.66 cm
• Height: 26.81 cm

First, put those numbers into the formula:

D = √(47.66² + 26.81²)

D ≈ 54.68 cm

Next, convert the result into inches:

54.68 ÷ 2.54 ≈ 21.53 inches

So, the monitor's screen size is approximately 21.5 inches.

If you're curious about how screen dimensions relate to pixel density, take a look at our Help Center guide on how to extend or mirror a screen. It explains how to calculate PPI using a related diagonal measurement formula.

Quick Tip: Use Your Phone's Scientific Calculator

You don't have to work through the equation on paper, either. Most smartphones have a calculator that can handle the math.

• iPhone: Open the Calculator app, tap the Change Mode button, and select Scientific. You can then use the square (x²) and square root (√) functions to complete the calculation.
• Samsung Galaxy: Open the Calculator app and switch to scientific mode if available. You'll find the functions needed to square numbers and calculate square roots.

For the example above, square 47.66 and 26.81 separately, add the results, and then find the square root. You should get approximately 54.68 cm.

Calculator layouts and available functions may vary depending on your device and software version.

Does Aspect Ratio Affect Monitor Size?

Yes, but perhaps not in the way you might think.

Aspect ratio describes the relationship between a screen's width and height. It doesn't change how monitor size is measured, but it does affect the screen's proportions.

For example, a 16:9 monitor is generally wider and shorter than a 16:10 or 3:2 display with the same diagonal measurement.

This is why looking at the diagonal size alone isn't always enough when planning a workspace. If you have a specific desk area or storage compartment in mind, check the actual width and height before choosing a monitor.

How to Find Your Monitor Size Without Measuring

Not in the mood to grab a ruler? There's another way to find out how big your monitor is, and it's often quicker.

Start by checking the model number. You'll usually find it on a label on the back of the monitor. Once you have it, visit the manufacturer's official website and look up the product specifications. The screen size is generally listed there.

Don't have the model number handy? Check the original packaging or user manual instead.

You can also try looking up your monitor through Windows or macOS display settings. Depending on your device and connection, the system may identify the monitor model. Once you have that information, you can search for its screen size online.

How Are Curved Monitors Measured?

Curved monitors can make measuring a little more confusing. A standard ruler or measuring tape won't necessarily follow the screen's surface, especially if you're trying to find its actual curved width or height.

If that's what you need, a flexible measuring method can help.

What You'll Need

Before getting started, prepare a few simple items:

• A roll of removable masking tape
• A measuring tape
• A pencil or fine-tip pen

One thing to check before applying tape: make sure the adhesive is suitable for your monitor's screen coating. Test a small piece in an inconspicuous area first, and confirm that it can be removed without leaving residue or damaging the surface. Avoid putting strong adhesive tape directly on the display.

Step-by-Step Measuring Method

1. Apply the Masking Tape

Place a strip of removable masking tape along the top or bottom edge of the curved screen. Leave a little extra tape extending beyond both sides.

2. Follow the Screen's Curve

Gently press the tape along the edge, allowing it to follow the screen's curvature. Try not to stretch or twist it, as this could affect the measurement.

3. Mark Both Endpoints

At each end of the screen, crease the tape where the visible display area stops. Carefully mark both positions with a pencil or fine-tip pen.

4. Remove and Straighten the Tape

Slowly peel the tape away and place it on a flat surface. Straighten it gently without stretching it.

5. Measure the Distance

Use your measuring tape to find the distance between the two marks. Repeat the process along the opposite edge if you also need to measure the screen's height.

Important: Measuring along the curved surface gives you the actual surface width or height, which can be useful when checking dimensions for accessories such as a custom screen protector.

However, surface measurements are different from straight-line measurements. The measurement method used for a curved display may also depend on the manufacturer's specifications or applicable measurement standards. If you simply want to identify the advertised screen size, checking the manufacturer's product specifications is the safest option.

Common Monitor Sizes and Their Screen Dimensions

Sometimes it's easier to compare a few numbers than measure everything yourself. The table below shows approximate screen widths and heights for several common monitor sizes.

All examples use a 16:9 aspect ratio and refer to the active display area only.

Monitor Size	Approx. Width	Approx. Height
13.3 inches	29.4 cm	16.5 cm
15.6 inches	34.5 cm	19.4 cm
17.3 inches	38.3 cm	21.6 cm
21.5 inches	47.6 cm	26.8 cm
23.8 inches	52.6 cm	29.6 cm
27 inches	59.8 cm	33.6 cm
32 inches	70.8 cm	39.8 cm

Keep in mind that these are theoretical estimates, not exact dimensions for every monitor. Actual screen width and height depend on the aspect ratio and panel specifications. The figures also exclude bezels, stands, and the outer casing.

Common Mistakes When Measuring a Monitor

Measuring a monitor isn't particularly difficult, but a few small mistakes can throw off your results. Keep these in mind before you start:

• Including the bezel:Only measure the active display area. Including the frame around the screen will give you a larger result than the actual screen size.
• Measuring width instead of diagonal:A monitor's advertised size refers to its diagonal measurement, not its horizontal width.
• Confusing screen size with overall dimensions:The visible display and the entire physical monitor are two different things. Check both if you're planning a desk setup or looking for a carrying case.
• Mixing measurement units:When using the Pythagorean theorem, make sure the width and height are in the same unit before calculating.
• Ignoring aspect ratio:Two monitors with the same diagonal size can have different screen proportions. Don't assume they'll take up the same amount of horizontal and vertical space.

Final Thoughts

Finding out how big your monitor is doesn't have to be complicated. A ruler or measuring tape is usually enough to measure the visible screen diagonally. If you already know its width and height, you can also use the Pythagorean theorem to calculate the diagonal.

And if you know the model number, checking the manufacturer's specifications may be even quicker.

Just remember that screen size and overall monitor dimensions aren't the same thing. The first refers to the diagonal of the active display area, while the second describes the physical size of the entire device.

Once you know both, comparing monitors and planning your workspace becomes a lot easier. If you're thinking about getting a new display, our guide on how to pick a monitor for your PC can help you figure out what else to look for.

FAQs

1. Do You Measure a Monitor Screen Diagonally?

Yes. Monitor screen size is measured diagonally from one corner of the active display area to the opposite corner. The bezel and outer frame aren't included.

2. Does Monitor Size Include the Bezel?

No. The advertised screen size generally refers to the visible display area, not the entire monitor. The bezel, housing, and stand aren't included in the diagonal measurement.

3. How Do I Find Out How Many Inches My Monitor Is?

You can check the manufacturer's product specifications or measure the visible screen diagonally with a ruler or measuring tape. If your measurement is in centimeters, divide it by 2.54 to convert it into inches.

4. Are Monitor Screen Size and Monitor Dimensions the Same?

No. Screen size refers to the diagonal length of the active display area. Overall monitor dimensions describe the physical width, height, and depth of the device, which may include the bezel and housing.