The calculator is useful for approximations, but I've been bitten a few times. The only real way to know, as always, is to measure it. The Dell/HP salesmen are

The calculator is useful for approximations, but I've been bitten a few times. The only real way to know, as always, is to measure it. The Dell/HP salesmen are worse, if you try to talk about power, especially if you do HPC. They will often flat-out refuse to believe that you're going to take 100 servers, stuff GPUs and all the RAM you can find in them, and run them at 100% for years on end.