Granted, the calculator is targeted at SMBs, so it's conceivable that said targets will come away with at least a better sense of what their carbon footprint looks like -- and can use it as a starting point to reduce its size through better practices.
Forrester Research has also come out with a calculator for measuring your green IT baseline, a term coined by Forrester that represents an annual estimate of the energy consumption, CO2 emissions, and financial costs of operating your IT within and outside of the datacenter.
[ Learn more about calculating your green IT baseline. ]
The calculator has you enter the number of various IT equipment you have at your organizations, from PCs and peripherals to servers and networking equipment, as well as CRAC and lighting in the datacenter. You need to supply the watts per asset used and the number of hours per year each pool of equipment is up and running. You also enter your CO2 emissions and price per kWh. You're then given a chart showing annual CO2 emissions and costs associated with powering your IT gear; it will also measure your PUE and DCIE.
Like the Rackspace calculator, Forrester's isn't comprehensive, but I think it can provide some value for organizations planning to embrace sustainable technology practices at their organizations. Taking some time to calculate the baseline will provide a starting point from which they can work to improve.
Have you found any useful, free online tools for assessing your company's carbon footprint?