C++ : Size of structure? : <p><strong>My c++ code</strong> </p>

<pre><code>#include &lt;iostream&gt;
using namespace std ;

struct Node {
    int data ;
    struct Node *next;
};

int main(){
    struct Node *head = NULL;
    struct Node *second = NULL;
    cout &lt;&lt; sizeof(struct Node);
}
</code></pre>

<p><strong>output to terminal</strong></p>

<pre><code>16
</code></pre>

<p>How is the size 16 ?
Size of int is 4bytes. 
How come it's multiplied by 4 ?
Please can anyone give detailed calculation ?
Thanks !</p>
