categorized answer QandAEditors Use the X, x and # format codes in printf and sprintf: <br> <pre> $num = 15; printf("%X\n", $num); # F printf("%x\n", $num); # f printf("%02x\n", $num); # 0f printf("%#x\n", $num); # 0xf printf("0x%02x\n", $num); # 0x0f </pre> The last example is excessive but it forces formatting for zero: <pre> printf("%#x\n", 0); # 0 printf("0x%02x\n", 0); # 0x00 </pre> 63074