---
title: "calculateWindowSizeClass"
description: "Calculates the window's [WindowSizeClass] for the provided [activity].

A new [WindowSizeClass] will be returned whenever a configuration change causes the width or
height of the window to cross a breakpoint, such as when the device is rotated or the window is
resized."
type: "composable"
---

<div class='type'>Composable Function</div>


<a id='references'></a>

<div class='sourceset sourceset-android'>Android</div>


```kotlin
@ExperimentalMaterial3WindowSizeClassApi
@Composable
fun calculateWindowSizeClass(activity: Activity): WindowSizeClass
```


Calculates the window's `WindowSizeClass` for the provided `activity`.

A new `WindowSizeClass` will be returned whenever a configuration change causes the width or
height of the window to cross a breakpoint, such as when the device is rotated or the window is
resized.




## Code Examples
### AndroidWindowSizeClassSample
```kotlin
@OptIn(ExperimentalMaterial3WindowSizeClassApi::class)
fun AndroidWindowSizeClassSample() {
    class MyActivity : ComponentActivity() {
        override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            setContent {
                // Calculate the window size class for the activity's current window. If the window
                // size changes, for example when the device is rotated, the value returned by
                // calculateSizeClass will also change.
                val windowSizeClass = calculateWindowSizeClass(this)
                // Perform logic on the window size class to decide whether to use a nav rail.
                val useNavRail = windowSizeClass.widthSizeClass > WindowWidthSizeClass.Compact
                // MyScreen knows nothing about window size classes, and performs logic based on a
                // Boolean flag.
                MyScreen(useNavRail = useNavRail)
            }
        }
    }
}
```