It's not explicitly documented; number_format also rounds:<?php$numbers = array(0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009);foreach ($numbers as $number) print $number."->".number_format($number, 2, '.', ',')."<br>";?>0.001->0.000.002->0.000.003->0.000.004->0.000.005->0.010.006->0.010.007->0.010.008->0.010.009->0.01