Byte conversion

There are a million little applets and forms out there to do byte conversions, but for whatever reason this is the one I have bookmarked. I'm sure full time performance testers can do this stuff in their head, but us part-timers need help every now and then. Perhaps I like it because it's a simple clean interface, and it shows me the conversion rates:

1 Byte = 8 Bit
1 Kilobyte = 1024 Bytes
1 Megabyte = 1048576 Bytes
1 Gigabyte = 1073741824 Bytes

Do you have one you prefer? Or perhaps another similar simple tool you use when testing?