Hyper-V RAM Calculator
Joeelway's blog links to a handy Hyper-V RAM Calculator you can use to plan your Hyper-V deployment. Easy to use:
Specify how much RAM is in the physical host machine. Add each guest VM and enter how much RAM (in GB) you want to allocate to the guest. The RAM utilized by the guest is calculated and the amount remaining on the host is presented. 
