About the Screen Size Checker
Screen Size Checker shows what your browser can tell about your display. At the top is the size of your browser window, updated live as you resize it, with the CSS breakpoint it falls in and its aspect ratio. Below are the screen size in CSS pixels, the real resolution in physical pixels with its common name such as Full HD or 4K, the device pixel ratio, aspect ratio, available area, colour depth, orientation and touch support. It also lists your language, time zone, whether your device asks for dark mode or reduced motion, and the browser identification string. One button copies a plain-text report for a support request or a bug report. The values are read on your device and nothing is sent to a server.
Updated September 2026
How to use the Screen Size Checker
- 1Open the page on the device you want to check. The values appear at once.
- 2Read the browser window size at the top. Resize the window or rotate the phone to see it change.
- 3Check the screen size, real resolution, pixel ratio and aspect ratio in the list below.
- 4Note your device class and CSS breakpoint if you are testing a website.
- 5Press Copy this report to paste the details into an email or a bug report.
Different kinds of size
A screen has several sizes and they are easy to mix up. The physical size in inches is fixed by the hardware. The resolution is the number of real pixels it has across and down. CSS pixels are a unit browsers use to keep websites readable, so a phone with a very high resolution still reports a small CSS width. The window size is the space inside the browser, and it is the one that decides how a website lays itself out.
This tool shows the ones your browser can report, and it labels each so you know which is which.
Useful for web design and testing
- Check the window width to see which breakpoint your page will use.
- Use the pixel ratio to decide how large images should be for sharp display.
- Rotate a phone or tablet to test both orientations.
- Compare devices by opening the page on each and copying the report.
- Test dark mode and reduced motion settings that your device reports.
When to send a report
Support teams and developers often ask for screen size, browser and device details when a page looks wrong. The copy button gives them everything in one message, including the browser identification string that shows the browser name, version and operating system. It is not private secret data, but it is specific to your device, so share it only with people you trust.
If something looks different on another computer, compare the window size and pixel ratio first. Many layout bugs appear only at certain widths or with high-density screens.
Related tools
Aspect Ratio Calculator resizes any width and height to a ratio, Image Resizer changes a picture to the size a screen needs, Unit Converter converts between inches, centimetres and pixels for print sizes, What Is My IP shows your public network address and Color Converter helps match colours between formats.
Features
- Live browser window size
- Screen size in CSS pixels and real pixels
- Common resolution names such as Full HD and 4K
- Device pixel ratio and aspect ratio
- CSS breakpoint and device class
- Orientation, touch points and colour depth
- Language, time zone, dark mode and reduced motion
- One-click copy of a full report
Frequently asked questions
What is my screen resolution?
Look at the line Screen resolution (real pixels). It multiplies the CSS screen size by the pixel ratio, so a phone with a screen size of 390 × 844 and a ratio of 3 has a real resolution of 1170 × 2532. Phones and some laptops report CSS pixels, which are smaller numbers than the real pixels.
What is the difference between screen size and window size?
The screen size is the whole display. The window size, also called the viewport, is the area inside your browser where the page is drawn. It changes whenever you resize the window, open toolbars or rotate the device, and it is the number that matters for responsive web design.
What is device pixel ratio?
It is how many real pixels are used for one CSS pixel. A ratio of 1 is a standard screen, 2 is a typical Retina or high-density display and 3 is common on modern phones. Higher ratios make text and images look sharper, and they need images with more pixels.
Why does the size change when I zoom the browser?
Zooming changes the CSS pixel size and the pixel ratio. When you zoom in, the window covers fewer CSS pixels and the ratio goes up, so the numbers change. Set the zoom to 100 percent to see the values for your normal view.
How do I find my aspect ratio?
It is shown next to the screen size. Common ones are 16:9 for most monitors and TVs, 16:10 for many laptops, 4:3 for older screens and about 19.5:9 for modern phones. The tool rounds to these well-known ratios if the numbers are close.
Can it tell me the physical screen size in inches?
No. Browsers do not know the physical size of a display, so they cannot report inches or centimetres. To get the diagonal, check your device's specification or measure the screen from corner to corner.
Is any of this information sent anywhere?
No. The values are read by your browser on your device and shown on the page. Nothing is uploaded or stored. The Copy button only places text on your own clipboard.