How to determine the memory footprint (size) of a variable?

Question

Is there a function in PHP (or a PHP extension) to find out how much memory a given variable uses? sizeof just tells me the number of elements/properties.

Answer 1

In answer to Tatu Ulmanens answer:

It should be noted, that $start_memory itself will take up memory (PHP_INT_SIZE * 8).

So the whole function should become:

function sizeofvar($var) {
    $start_memory = memory_get_usage();
    $var = unserialize(serialize($var));
    return memory_get_usage() - $start_memory - PHP_INT_SIZE * 8;
}

Sorry to add this as an extra answer, but I can not yet comment on an answer.

Update: The *8 is not definate. It can depend apparently on the php version and possibly on 64/32 bit.