Measuring across your monitor's width won't give you its advertised screen size, and including the frame changes the result too. Screen size is the diagonal distance across the visible panel. Here's how to measure it, find the size without a tape measure, and check the separate dimensions that determine whether it fits your desk.
Measure the visible screen diagonally
A corner-to-corner measurement gives you a flat monitor's screen size.
Place the start of a ruler or tape measure at the bottom-left corner of the visible screen, keeping the tool from pressing against or scratching the panel.
Extend it to the top-right corner of the visible screen, excluding the bezel, housing and stand. The other pair of opposite corners works too.
Read the distance in inches.
For a metric measurement, divide centimeters by 2.54 or millimeters by 25.4 to get inches. A diagonal of 68.6 cm is approximately 27 inches.
If your measurement doesn't match the advertised size
Including the frame measures beyond the visible panel and changes the result.
Repeat the diagonal measurement using only the corners of the visible screen. Measuring straight across gives you its width, which is a different measurement from its advertised diagonal.
Compare your result with the exact model's published viewable diagonal. Marketed size classes and precise viewable measurements are distinct, so check the model-specific measurement notes for size-class differences and rounded corners.
For a curved monitor, use the manufacturer's published diagonal for your exact model.
Find the size without a measuring tape
Your monitor's full model number leads you to its official screen-size specification.
- 1.Read the manufacturer's label on the back or underside of the monitor. Use a phone photo to read a hard-to-reach label.
- 2.Record the complete model or product code, including any suffixes. If the label is inaccessible, check the original box, manual or purchase documents.
- 3.Search the manufacturer's website for that exact model and open its product specifications or user guide. Don't infer the size from digits in the model name; model numbers are not a universal sizing standard.
- 4.Read the screen-size or diagonal specification. On Dell's U2725QE product page, the product summary lists Diagonal Size as 27 inches, and Viewable Screen Size under Tech Specs is also 27 inches.
Your computer can help identify the display
In Windows 11, open Settings > System > Display > Advanced display. Select the relevant monitor when several are connected. Use its displayed name to find the exact model's official specifications; if the name is generic, use the hardware label instead.
For a MacBook Pro's built-in screen, choose Apple menu > About This Mac. Match the complete model description to Apple's MacBook Pro model-identification page, then follow the matching Tech Specs link. The Mac's model does not identify a separately connected external monitor.
On a Chromebook, select the time at the bottom right, then open Settings > Device > Displays. Select the external monitor's name and use it to find the manufacturer's specifications. A generic name or Built-in Display does not identify the panel.
Resolution, scaling and refresh rate describe how the display operates; they do not establish its physical size in inches. For that, use a physical measurement or the exact model's specifications.
Calculate the diagonal from width and height
For a flat rectangular screen, calculating the diagonal from its two sides gives you another route when opposite corners are hard to reach. Use the visible panel's dimensions, excluding the frame and enclosure.
Measure the visible screen's width and record it as W.
Measure its visible height and record it as H, using the same units as the width.
Square each measurement to begin the calculation diagonal = √(W² + H²).
Add the two squared values.
Take the square root of that total to get the diagonal.
If your measurements are in centimeters, divide the resulting diagonal by 2.54 to convert it to inches.
If you cannot measure both visible edges accurately, use the exact model's official specifications.
Check the whole monitor for desk space
Overall dimensions tell you whether the monitor fits your space; find them in the exact model's specifications or measure them separately from the screen diagonal.
- 1.Measure the housing's full width, including the frame.
- 2.Measure the monitor's overall height with the stand installed.
- 3.Measure its depth with the stand installed.
Frequently Asked Questions
Does the diagonal method work for laptop screens?
Yes. Measuring the visible diagonal also works for flat laptop screens, all-in-one computers and portable monitors, regardless of operating system.
Can a screenshot tell me my monitor's size?
No. A screenshot's pixel dimensions do not independently establish physical inches. Use a physical measurement or the exact monitor model's specifications.
Can I measure my monitor with an iPhone?
Yes, as an estimate, using Measure on a compatible iPhone. Open Measure and scan the monitor. Align the center dot with one visible screen corner and tap +. Move to the opposite visible corner and tap + again. Read the approximate distance, using the panel corners rather than the outer frame.