How to get UI element size property with Unity UI toolkit

I'm trying to get and store the width of a UI element (using the Unity UI toolkit) for later calculation:

int width = SomeGroupBox.style.width.value; 

Where the group box is acquired by SomeGroupBox = GetComponent<UIDocument>().rootVisualElement.Q<GroupBox>("NameOfGroupBox"); .

But Unity refuses to give me the width and showed:

Error CS0029 Cannot implicitly convert type 'UnityEngine.UIElements.Length' to 'int'

Explicitly casting it into int also did not work, neither does the float or long type.

Is there a way to use the UnityEngine.UIElements.Length type as int?

I think you just need another value there

float width = SomeGroupBox
                  // https://docs.unity3d.com/ScriptReference/UIElements.VisualElement-style.html
                  // -> returns UIElements.IStyle
                  .style
                  // https://docs.unity3d.com/ScriptReference/UIElements.IStyle-width.html
                  // -> returns UIElements.StyleLength
                  .width
                  // https://docs.unity3d.com/ScriptReference/UIElements.StyleLength-value.html
                  // -> returns UIElements.Length
                  .value
                  // https://docs.unity3d.com/ScriptReference/UIElements.Length-value.html 
                  // -> returns float
                  .value;  

To get the dimensions of a UI element it is recommented to use resolvedStyle

So in your case:

SomeGroupBox = GetComponent<UIDocument>().rootVisualElement.Q<GroupBox>("NameOfGroupBox");

int width = SomeGroupBox.resolvedStyle.width;