How to Measure Screen Size — Laptop, Monitor, TV & Phone
Measure a laptop, monitor, TV or phone screen correctly: exclude the bezel, convert cm to inches, calculate the diagonal, or use a bank card without a ruler.
Quick answer
Measure only the visible display from one corner to the opposite corner, diagonally; exclude the bezel, casing and stand. Record the result in inches, or divide centimeters by 2.54. If you have no tape measure, calibrate this screen with a standard bank card.
Measure and verify your screen
The number sold as screen size is the diagonal of the visible display, not its width and not the outside edge of the device. ENERGY STAR product data keeps “diagonal viewable screen size” separate from viewable width, height and area for the same reason. See the ENERGY STAR field definitions.
What did you measure?
Values stay in this browser and are not added to the URL or sent to ScreenSize.net.
Enter the corner-to-corner visible measurement.
How to measure screen size in four steps
- 01
Reveal the visible edge
Turn the display on and use a plain image so you can distinguish pixels that light up from a black bezel or border under edge-to-edge glass.
- 02
Choose opposite visible corners
Start at one corner of the active display and finish at the corner furthest away. Do not start from the casing, lid, frame, stand or protective case.
- 03
Keep the diagonal straight
Hold the tape straight across the face without following an edge. Keep metal hooks and sharp ruler edges just above the panel so they do not scratch it.
- 04
Record the unit and repeat
Repeat once to catch a misplaced endpoint. If you measured centimeters, divide by 2.54 for inches; one inch is exactly 25.4 mm under the NIST definition.
Use a standard card as the reference
A standard ISO ID-1 bank or identification card is 85.60 mm wide and 53.98 mm high. Match the card's physical width to the outline in the card method above. The browser can then convert its screen coordinates into a calibrated physical estimate. The card dimensions come from ISO/IEC 7810.
Calibration is stored only in this browser. Nothing from the form or card is uploaded, and no camera is used.
CSS pixels are normally not physical pixels or reliable physical inches on a screen. Browser zoom, operating- system scaling and moving to another display can invalidate an earlier match. The W3C explanation of CSS units describes that distinction.
What changes for laptops, monitors, TVs and phones?
The visible diagonal is measured the same way, but it is often not the dimension you need for a bag, mount, furniture opening or fitted accessory.
| Device | Screen-size measurement | Measure separately when you need… |
|---|---|---|
| Laptop | Visible panel diagonal | Body width, depth and thickness for a bag; exact model and panel code for a replacement |
| Monitor | Visible panel diagonal | Outside width, stand depth, height range, weight and mounting pattern |
| TV | Visible picture diagonal | Cabinet width and height, feet spacing, stand height and cable clearance |
| Phone or tablet | Published diagonal; check the rounded-corner note | Complete device dimensions for a case; product-specific glass dimensions for a protector |
Rounded corners need a specification note. Apple, for example, states that one rounded iPad display is measured as its enclosing standard rectangle and that the actual viewable area is smaller. Read the manufacturer note.
Accessory measurements are vendor-specific. 3M asks for the viewable opening on a raised-bezel display but the full glass dimensions on a flat-front display. Follow the accessory measuring guide.
Calculate diagonal, width or height
Width, height and diagonal form a right triangle. Use measurements in the same unit throughout; converting the final diagonal does not change the result.
D = √(W² + H²) W = D × A ÷ √(A² + B²) H = D × B ÷ √(A² + B²) The diagonal may not answer your real question
Comparing visible screen area
Record diagonal and aspect ratio, then use the screen size comparison. Equal diagonals can have different width, height and area.
Checking a desk, wall or TV stand
Measure the complete product and stand. A panel-only width calculated from the diagonal cannot guarantee that a particular model fits.
Buying a case, filter or replacement panel
Find the complete model identifier and follow the vendor's measurement diagram. Windows shows the device model under Settings → System → About. Microsoft documents the steps.
Measuring a small object on screen
Calibrate once, then use the online ruler instead of treating a CSS inch as a physical inch.
Screen size is not resolution, viewport, DPR or PPI
| Measurement | What it describes | Typical unit |
|---|---|---|
| Screen size | Physical diagonal of the visible display | in / cm |
| Resolution | The panel's pixel grid | pixels |
| Viewport | Browser area available to a web page | CSS px |
| Device pixel ratio | Physical-pixel scale behind one CSS pixel | ratio |
| PPI | Pixel density produced by resolution and physical size | pixels/in |
Common screen measurement mistakes
- Including the bezel
Start at the visible panel edge, not the outside corner of the device.
- Calling width the screen size
The advertised size is diagonal; width alone will be smaller.
- Mixing centimeters and inches
Keep one unit through the calculation, then convert the final result.
- Inferring inches from resolution
The same pixel resolution can appear on several physical sizes.
- Assuming every CSS inch is physical
Calibrate the current display before using an on-screen reference.
- Using the diagonal for fit
Furniture, bags and mounts depend on the complete product dimensions.
Questions that change the measurement
- Does screen size include the bezel?
- No. Screen size describes the visible display diagonal. Measure the bezel and casing separately when overall fit matters.
- Do you measure a screen corner to corner?
- Yes—from one visible corner to the opposite visible corner, in a straight diagonal line.
- Can I find screen size without measuring it?
- Look up the complete model on the manufacturer's official specification page. If the model is unavailable, use the calibrated card method above as an estimate and verify before purchasing a fitted product.
- Why can my result differ from the advertised size?
- Check that both endpoints are on the visible panel, that the tape is straight and that the units match. For a rounded display, also check whether the manufacturer quotes the diagonal of an enclosing rectangle.
- Can a website detect physical screen inches automatically?
- Not reliably. Browsers expose screen coordinates, but their CSS units do not guarantee the display's physical dimensions. A known physical reference is needed for a calibrated estimate.
Sources
- ENERGY STAR display specification fields — checked
- NIST SI Units — Length — checked
- ISO/IEC 7810 identification card dimensions — checked
- W3C CSS units — checked
- Apple iPad Pro display measurement note — checked
- Microsoft Support — find device name and model — checked
- 3M measuring guide for monitors and laptops — checked
Content reviewed .
Online Ruler
A real-size on-screen ruler in centimeters and inches. Calibrate once with a bank card for true 1:1 accuracy on any display.
Related tools
- Screen Size Comparison Compare phone, tablet, laptop and monitor screens as proportional overlays — or against your own screen. True-size mode shows devices at real physical size.
- Aspect Ratio Calculator Calculate and simplify aspect ratios, find missing dimensions, and match against common display formats like 16:9, 16:10 and 21:9 — with a live preview.
- PPI Calculator Calculate PPI from resolution and screen size. Instant results with the formula worked through your numbers, plus physical dimensions and dot pitch.
- Device Screen Sizes Browse sourced screen sizes, resolutions, CSS viewports, DPR and PPI for phones, tablets and laptops, with links to model-level specifications.