Reading your screen resolution
The big number at the top is your physical resolution — the number of pixels the panel really has, such as 1920 × 1080 or 2560 × 1440. That is the figure on the box and the one to quote when someone asks what resolution your monitor is. The tool works it out from the CSS resolution and the device pixel ratio, compensating for browser zoom, then matches it against a list of known panels so a MacBook, iPhone or common monitor is named correctly.
Below it, three panels break down everything the browser knows:
- Screen — physical and CSS resolution, device pixel ratio, the space left after the taskbar or dock, aspect ratio, colour depth and orientation.
- Browser window & zoom — the viewport a web page actually gets, the visible area after pinch-zoom or an on-screen keyboard, the window's size and position, the estimated page zoom and your operating system's scaling.
- Capabilities — colour gamut, HDR, whether you have more than one screen, touch support and pointer type.
Everything updates live. Resize the window, rotate your phone, drag the browser to another monitor or press Ctrl + and the changed values flash so you can see cause and effect.
Physical pixels, CSS pixels and device pixel ratio
Modern screens are too dense to show web pages at one pixel per pixel — text would be microscopic on a phone. So browsers work in CSS pixels, and the device pixel ratio (DPR) says how many real pixels make up one CSS pixel in each direction.
| Device | Physical | DPR | CSS resolution |
|---|---|---|---|
| 24″ 1080p monitor, 100% | 1920 × 1080 | 1 | 1920 × 1080 |
| 15.6″ 1080p laptop, 125% scaling | 1920 × 1080 | 1.25 | 1536 × 864 |
| 27″ 4K monitor, 150% scaling | 3840 × 2160 | 1.5 | 2560 × 1440 |
| iPhone 15 | 1179 × 2556 | 3 | 393 × 852 |
On a desktop the DPR is the product of two settings: display scaling in Windows Settings or macOS Displays, and the browser's page zoom. The tool separates the two by comparing the window's outer size, which zoom doesn't affect, with the viewport, which it does. So a DPR of 1.375 is read as 125% scaling plus 110% zoom rather than a mystery number. Firefox scales both measurements together, so there it shows 100% zoom and folds any zoom into the scaling figure; side-docked developer tools also throw the estimate off.
Developers: media queries and window.innerWidth use CSS pixels, so the viewport figure and the Tailwind or Bootstrap breakpoint shown are the ones your layout responds to.
Working out PPI and pixel pitch
No browser can tell how big your screen physically is, so pixel density needs one fact from you: the diagonal. Choose a common size or type your own — 27, 15.6" or 68.6 cm all work — and the calculator gives:
- Pixels per inch (PPI) — the diagonal pixel count divided by the diagonal length. Around 90–110 is typical for desktop monitors, 140–220 for sharp laptop screens, and 400 or more for phones.
- Pixel pitch — the distance between pixel centres in millimetres, the figure monitor spec sheets quote.
- Visible width × height — handy for checking a monitor will fit a desk or a TV a wall.
- Distance where pixels vanish — beyond this, someone with normal vision (one arc-minute of acuity) can no longer pick out individual pixels. Sit closer and a higher resolution is a visible upgrade; sit further back and it isn't.
A Mac set to a scaled “looks like” resolution renders at a size that isn't the panel's native one, so the physical figure here can differ from the spec sheet. Type the native resolution into the override box for an exact PPI. To measure real-world sizes on screen, calibrate the online ruler.
Which resolution is right for what
For a monitor, resolution only makes sense together with size and viewing distance. 1080p is sharp at 24 inches and looks soft at 27. 1440p is the sweet spot for 27-inch gaming and office monitors, at about 109 PPI with no scaling needed. 4K at 27 inches is 163 PPI and wants 150% scaling for readable text, but everything becomes crisply printed-looking; at 32 inches it works at 125%. Ultrawide 3440 × 1440 is a 1440p screen stretched to 21:9 for games and timelines.
On laptops, a high-DPI panel with scaling looks sharper than a native low-resolution one, at a small cost in battery life. For games, the GPU has to render every physical pixel, so a 4K screen needs roughly two and a quarter times the graphics power of 1440p for the same frame rate — check what your display can actually show with the refresh rate test, and look over a new panel with the dead pixel test.
Frequently asked questions
What is my screen resolution?
It's the large number at the top of this page, for example 1920 × 1080. That is the physical resolution — the real pixels on your panel. Websites see a smaller CSS resolution when Windows or macOS scaling is above 100%, or on phones, and both figures are shown along with the device pixel ratio that links them.
Why does my screen resolution look lower than my monitor's spec?
You are probably reading the CSS resolution. With 125% Windows scaling, a 1920 × 1080 laptop reports 1536 × 864 to websites; a 4K monitor at 150% reports 2560 × 1440. That is normal, and the physical resolution here should match the spec. If it doesn't, check the resolution in your display settings is set to the recommended (native) value.
Can a website detect my browser zoom level?
Only approximately. There's no official zoom API. This tool compares the window's outer width, which zoom doesn't change in Chrome, Edge and Safari, with the viewport width, which it does. That gives a reliable estimate at standard zoom steps. Firefox and phones don't expose enough to separate zoom from scaling, so there the figure is marked accordingly.
What is device pixel ratio (DPR)?
DPR is the number of physical pixels per CSS pixel along each axis. A DPR of 2 means every CSS pixel is drawn with a 2 × 2 block of real pixels, which is what makes Retina screens look sharp. It is set by your operating system's display scaling multiplied by the browser zoom, and developers use it to serve sharper images.
How do I find my screen size in inches?
A browser can't measure it, so check the model number on the back of the monitor, the laptop's spec page or the original box. Screen size is always the diagonal of the visible area. Enter it in the PPI calculator and you'll see the physical width and height, pixel density and pixel pitch worked out from your resolution.
Is 1440p or 4K better for a 27-inch monitor?
For gaming, 1440p: it runs at about 109 PPI with no scaling, and needs far less graphics power for high frame rates. For text, photos and office work, 4K is noticeably sharper at 163 PPI but needs 150% scaling to keep text readable. At a normal desk distance both look good; 4K mainly wins when you sit close.