$bytes() is well and good but it should be considered a convenience, not a substitute for gaps in understanding of basic things; knowing the relations between bytes, kb, mb etc is essential not only to every programmer/scripter, but to every computer user beyond the novice level. By not telling you about $bytes(), I hoped I'd make you learn these conversion rules from those Google results. I still hope that worked, despite you getting the $bytes() answer.
and couldent find that on the net.
However you could find it in the help file, in the most obvious section for this: Text and Number Identifiers
. I'm saying that to emphasise the importance of being able to find things out on your own, in the same (or even less) time it would take you to ask other people. This may not always be possible of course, but you should always try and find out; you have much more to gain from this in the long run.