What screen size actually measures
The advertised size of a monitor, laptop, TV, phone, or tablet is normally the diagonal of the visible display area. Measure from one visible corner to the opposite visible corner. Keep the tape or ruler on the panel itself and exclude the bezel, frame, keyboard deck, stand, and device body.
How to measure screen size step by step
Turn the display off so the edge of the active panel is easier to see. Place the zero mark at one visible corner, run the tape in a straight diagonal line to the opposite visible corner, and record the result in inches or centimeters. If you measured centimeters, divide by 2.54 to convert to inches. Repeat once to catch alignment mistakes.
How to measure a laptop screen
Open the laptop normally and measure only the illuminated panel from corner to corner. Do not include the black border, webcam area, lid, hinge, or keyboard. If you are buying a replacement panel or privacy filter, also verify the exact model number because two laptops with the same advertised diagonal can use different panel shapes, connectors, or mounting points.
How to measure a monitor screen
Measure the visible monitor panel diagonally, not the outside casing. Then check the current resolution and aspect ratio in the operating-system display settings. Use the Screen Size Calculator when you want the estimated physical width, height, and PPI for a 16:9, 16:10, ultrawide, or other monitor shape.
How to measure a TV screen
TV size is also measured diagonally across the visible picture area. For wall mounting or furniture fit, the advertised diagonal is not enough: measure the complete outside width and height separately, then include the stand, feet, cable clearance, soundbar, ventilation, and mounting hardware in the space plan.
How to measure a phone or tablet screen
Measure the visible display diagonally without including the case or device body. Rounded corners and camera cutouts mean the fully viewable rectangle can be slightly smaller than the stated diagonal. For responsive web testing, use the CSS viewport and DPR rather than trying to convert the physical diagonal into a breakpoint.
How to calculate screen width and height
To estimate physical dimensions from diagonal D and aspect ratio W:H, calculate width as D × W ÷ √(W² + H²) and height as D × H ÷ √(W² + H²). A 27-inch 16:9 panel is about 23.5 inches wide and 13.2 inches high before adding the bezel. The calculator applies this geometry automatically and can also estimate pixel density from resolution.
Common screen measurement mistakes
Do not measure straight across the width and call that the screen size. Do not include the bezel, round a centimeter result as though it were inches, or assume every screen with the same diagonal has the same width. Also keep physical screen size separate from resolution, viewport size, DPR, and PPI: each answers a different question.
Measurement examples
Diagonal size to width and height
These are approximate visible-panel dimensions for a 16:9 screen. The bezel and stand add to the product's outside dimensions.
| Diagonal | Approx. width | Approx. height | Common context |
|---|---|---|---|
| 24 inches | 20.9 in / 53.1 cm | 11.8 in / 29.9 cm | Compact desktop monitor |
| 27 inches | 23.5 in / 59.8 cm | 13.2 in / 33.6 cm | Work or gaming monitor |
| 32 inches | 27.9 in / 70.8 cm | 15.7 in / 39.8 cm | Large desktop monitor |
| 55 inches | 47.9 in / 121.7 cm | 27.0 in / 68.5 cm | Medium living-room TV |
| 65 inches | 56.7 in / 143.9 cm | 31.9 in / 80.9 cm | Large living-room TV |
| 75 inches | 65.4 in / 166.0 cm | 36.8 in / 93.4 cm | Large TV or presentation display |
Formula for any aspect ratio
Width = D × W ÷ √(W² + H²)
Height = D × H ÷ √(W² + H²)
D is the diagonal. W:H is the aspect ratio, such as 16:9 or 21:9.
Skip the manual math
Enter the diagonal and resolution to estimate width, height, aspect ratio, area, and pixel density.
Open Screen Size CalculatorChecklist
- ✓ Turn the display off so the panel edge is clear
- ✓ Measure visible corner to visible opposite corner
- ✓ Keep the tape straight across the panel
- ✓ Exclude the bezel, frame, case, and stand
- ✓ Record the unit as inches or centimeters
- ✓ Divide centimeters by 2.54 when inches are needed
- ✓ Check the aspect ratio before estimating width and height
- ✓ Measure outside dimensions separately for desk or wall fit
- ✓ Verify the exact model for replacement parts
- ✓ Use viewport and DPR for web-layout testing