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What is my browser window size?

Detect your current browser window size in pixels. Free online tool — no sign-up. Clear formulas and worked examples. Runs locally in your browser.

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How to use

1

Open on the device to measure

Load the tool in the browser window or display you care about.

2

Read the live metrics

Check width × height in CSS pixels (screen and/or viewport, depending on the page).

3

Resize and compare

Resize the window or switch displays, then refresh the readout for responsive checks.

Window size specification

Version 1.0.0 · Engine tested

Calculation status
  • Engine tested 1 published cases
  • Named expert review Not performed
  • Calculation version 1.0.0

Review policy

Definition
Window size tools report the browser window or viewport dimensions in CSS pixels.
What it calculates
innerWidth/innerHeight (or equivalent viewport metrics) for the current browser window.
Inputs
  • None — live window metrics
Outputs
  • Viewport width × height in CSS pixels
Formula
size = window.innerWidth × window.innerHeight

This tool reports your current browser window size — the viewport width and height in pixels. Unlike screen resolution, window size reflects the visible browser area excluding the taskbar, browser chrome, and OS UI.

What the tool shows

Property Description
Window width Viewport width in pixels
Window height Viewport height in pixels
Outer width Full window including toolbars
Outer height Full window including title bar

Window size vs. screen resolution

Window size Screen resolution
Measures Browser viewport Entire display
Changes when User resizes browser OS display settings
Used for CSS media queries Hardware specs

CSS media query breakpoints

Common breakpoints to test against your window size:

/* Mobile */
@media (max-width: 576px) { }

/* Tablet */
@media (max-width: 768px) { }

/* Desktop */
@media (min-width: 992px) { }

/* Large desktop */
@media (min-width: 1200px) { }

Resize your browser and watch the window size change to find breakpoint boundaries.

Use cases

  • Test responsive layouts at specific viewport sizes
  • Verify mobile breakpoints during development
  • Debug layout issues at particular window dimensions
  • Compare with screen resolution
Assumptions
  • Updates as the window is resized.
  • Local only.
Units
  • px
Boundary conditions
  • Browser chrome reduces viewport relative to outer window size.
Example
Resize to a phone-like width → innerWidth near 390 px
Validation cases
  • Maximize window → Larger innerWidth/innerHeight
Sources
  • CSSOM View — Window dimensions
Calculation version
1.0.0
→ Screen resolution › → Pixel ruler ›

Frequently asked questions

Key distinctions behind the tool.

innerWidth vs outerWidth?

innerWidth is the viewport; outerWidth includes browser chrome.

Why does mobile show a different width?

Mobile browsers use a layout viewport and scaling; CSS pixels are what layouts use.