bcmul

Multiply two arbitrary precision number (PHP 4, PHP 5)
string bcmul ( string left_operand, string right_operand [, int scale] )

Multiply the left_operand by the right_operand.

left_operand: The left operand, as a string.
right_operand: The right operand, as a string.
scale: This optional parameter is used to set the number of digits after the decimal place in the result. You can also set the global default scale for all functions by using bcscale().

Returns the result as a string.

<?php
echo bcmul('1.34747474747', '35', 3); // 47.161
echo bcmul('2', '4'); // 8
?>