memory_limit_test.php

<?php

for ($i = 1; $i < 200; $i++) {
    $a = load($i);

    echo "You have allocated {$i}M (".memory_get_usage().") memory in this php script\n";
    unset($a);
}

function load($i)
{
    $a = str_repeat('0', $i * 1024 * 1024); // allocating 10 chars times million chars
    return $a;
}