But is there much of a performance hit when using Double instead of Long? Reading that link you provided, a Long is 4 bytes long while a Double is 8 bytes long. There is a significant performance hit when using Double (or Single), not because of the different number of bytes but because Doubles are floating point and use a different representation. Longs are just simple binary numbers and are much more straight forward to process. However it depends on what you are doing as to whether it really matters to your application. If you are doing massive, complex calculations where a large part of the processing time is spent just calculating then it will make a big difference, but if it's just displaying a simple screen or reading a few rows from a database etc you won't notice any difference at all. Will there be much of a performance hit when using a Double instead of a Long variable type? I wouldn't worry about it too much. I know the purist's will come down on me for saying this, but the reality is you can spend a lot of time writing code that will be really efficient in order to save a couple of milliseconds and maybe a meg or two of RAM. I would rather see that development time go towards better application testing and documentation. If you are writing something that is computationally arduous, you should probably use a lower level language like C++ as opposed to