512MB System Memory:
Your -heapsize should be: "262144″
1GB System Memory:
Your -heapsize should be: "524288″
2GB System Memory:
Your -heapsize should be: "1048576″
3GB System Memory
Your heapsize should be:"1572864"
4GB System Memory
Your heapsize should be:"2097152"
5GB System Memory
Your heapsize should be:"2621440"
6GB System Memory
Your heapsize should be:"3145728"
7GB System Memory
Your heapsize should be:"3670016"
8GB System Memory
Your heapsize should be:"4194304"

I have 4GB Memory, and I know that Windows needs some of the GB, I don't want to use all of it.