Physical Pixels vs Logical Pixels: Interactive Guide with Your Screen's Real Numbers

Your Screen's Numbers — Live

Before diving into theory, here are your screen's actual values right now:

These values come from your browser's actual APIs — no guessing. The "estimated" physical resolution is calculated as screen.width × DPR and screen.height × DPR; it matches the real hardware in most cases but can be affected by GPU virtual super-resolution or browser zoom. If DPR is 1.0, your physical and logical pixels are identical. If it is higher, there is a transformation happening between what software sees and what your screen displays. Use our screen coordinates tool to see how this affects mouse positions in real time.

What Are Physical Pixels?

A physical pixel (also called a device pixel) is a single, real dot on your screen hardware. It is the smallest addressable element of your display. On an LCD panel, each physical pixel is made up of three sub-pixels (red, green, blue), and together they produce one color dot.

Your monitor's physical resolution tells you exactly how many of these dots it has:

• A 1920×1080 monitor has 2,073,600 physical pixels
• A 3840×2160 (4K) monitor has 8,294,400 physical pixels
• An iPhone 15 Pro has 2,556×1,179 physical pixels in a 6.1-inch screen

Physical pixels never change for a given display. A 4K monitor always has 3840×2160 physical pixels regardless of your Windows scaling settings. The hardware is fixed.

For a comparison of what different physical pixel counts mean for coordinate systems, see our Screen Resolution Comparison guide.

What Are Logical Pixels (CSS Pixels)?

A logical pixel (also called a CSS pixel, device-independent pixel (DIP), or point on macOS) is a unit of measurement that software uses for layout. It is an abstraction — a logical pixel is not necessarily one physical pixel.

On a standard 1080p monitor at 100% scaling, one logical pixel = one physical pixel. Simple. But on a Retina MacBook Pro with DPR 2, one logical pixel = a 2×2 grid of physical pixels (4 physical pixels total). On a Windows 4K display at 150% scaling, one logical pixel = a 1.5×1.5 area of physical pixels.

Visual comparison — each colored square is one physical pixel. One logical pixel maps to different grids depending on DPR:

Device Pixel Ratio: The Bridge Between Physical and Logical

The Device Pixel Ratio (DPR) is the multiplier that converts between logical and physical pixels:

physical_pixels = logical_pixels × DPR

Examples (width only):
  1920 logical × DPR 1.0 = 1920 physical  (standard 1080p)
  2560 logical × DPR 1.5 = 3840 physical  (4K at 150% scaling)
  1440 logical × DPR 2.0 = 2880 physical  (MacBook Retina)

In JavaScript, you can read your DPR with window.devicePixelRatio. This value is read-only — it is determined by your display hardware and OS scaling settings.

DPR Is Not Always an Integer

Windows commonly uses fractional DPR values: 1.25 (125%), 1.5 (150%), 1.75 (175%). macOS uses exactly 2.0 for Retina displays. Android devices use various values (1.5, 2.0, 2.625, 3.0, 3.5, 4.0). Fractional DPR means that logical pixels do not map cleanly to physical pixels — one logical pixel might cover parts of multiple physical pixels, which is why text rendering on Windows at 125% scaling can look slightly blurry.

For how DPR interacts with DPI scaling on Windows and breaks automation scripts, see our DPI Scaling & Coordinates guide.

DPR by Device: MacBook, Windows, Android, iPhone

Common devices and their DPR values:

What This Means for Screen Coordinates and Automation

So what does this mean in practice?

• Automation tools disagree on coordinates. PyAutoGUI without DPI awareness uses logical coordinates; the Windows API GetCursorPos returns physical ones (for DPI-aware processes). Mix them up and every position is off by the DPR factor. Our PyAutoGUI Coordinates guide has the fix.
• Screenshots capture physical pixels. On a 4K display at 150% scaling, a screenshot is 3840×2160 — not 2560×1440. Trying to locate a UI element by its logical coordinates in that screenshot? Multiply by DPR first.
• CSS coordinates are always logical. Set left: 100px; top: 200px and those are logical pixels — the browser converts them to physical pixels behind the scenes. That is why getBoundingClientRect() returns CSS pixels.
• Multi-monitor setups can have mixed DPR. A Retina laptop screen (DPR 2) next to a standard external monitor (DPR 1) means the same coordinate maps to different physical spots on each display. Our Multi-Monitor Coordinates guide covers this.

Quick Reference: Which Coordinate System Am I Using?

Frequently Asked Questions