Count number of iterations in a foreach loop

foreach ($Contents as $index=>$item) {
  $item[$index];// if there are 15 $item[number] in this foreach, I want get the value : 15
}

You don't need to do it in the foreach.

Just use count($Contents).

If you just want to find out the number of elements in an array, use count. Now, to answer your question...

How to calculate how many items in a foreach?

$i = 0;
foreach ($Contents as $item) {
    $item[number];// if there are 15 $item[number] in this foreach, I want get the value : 15
    $i++;
}

If you only need the index inside the loop, you could use

foreach($Contents as $index=>$item) {
    // $index goes from 0 up to count($Contents) - 1
    // $item iterates over the elements
}

count($Contents);

or

sizeof($Contents);