In the process of looking into carbon calculators for buildings as a behind-the-scenes assistant for the EBN feature article "Counting Carbon: Understanding Carbon Footprints of Buildings," I took a short detour into the wider carbon calculator world. While construction calculators may still be rare, the Web offers a multitude of general carbon calculators for businesses and households and also specialized calculators for everything from wineries to land remediation activities. It seems everyone is getting into the act — utilities, environmental groups, oil companies, government agencies, and offset providers (especially offset providers) are all offering up their own calculators. These vary widely in their approach, scope, level of complication, rigor, transparency, visual appeal, and results — including what aspect of household or business operations is the greatest contributor to total emissions. The primary value of these simple calculators is getting people thinking about the issue and providing some motivation for change, but the system should at least be accurate enough to help users develop a reasonable sense of priorities for action. The ideal calculator would provide default values using average data while allowing users to improve the results by providing their own actual data on utility bills (including gallons, therms, kWh, not just dollars), vehicle fuel efficiency, miles driven, flights taken, and other behavioral characteristics. The ideal calculator would also provide tips for next steps, and allow users to track efforts over time, as well as test the likely impact of different strategies. Even better would be if you could dig behind the displayed answers and see what all the assumptions were underlying them — a major bonus for geeks like me. EBN did not attempt a comprehensive review of lifestyle calculators, or comparison of results (especially once we realized what a rabbit hole we'd be entering). A little browsing on the web shows how many others have tried variations on that theme — and how hard it can be. Also, new calculators pop up daily. The calculators below are just a few that we thought rose to the top while wandering through the morass of options. For a more in depth review (though still by no means comprehensive) try Consumer Reports' review of travel results, the Home Energy Saver table outlining the scope covered by a range of calculators, or check out the Earth Charter Initiative's list of calculators available by country. We'd love to hear of any truly thorough reviews you know of, or what calculators you think are best. A few notable calculators in the mix are the following:

• Low Impact Living's Environmental Impact Calculator, which provides a comparative assessment of a range of impacts, not just carbon emissions; suggests actions; and lets users save and update their profiles. (In contrast, the Ecological Footprint Calculator has an animated custom avatar, but I'm not convinced it provides much life-changing value.)
• The CoolClimate Carbon Footprint Calculator, which considers a wider range of activities at a detailed level. Inputs include what users eat and purchase as well as the more typical questions about the user's house, based on expenditures, and comparison with national and "similar household" averages. The calculator was developed by the Berkeley Institute of the Environment (BIE), at the University of California, Berkeley).

• Safe Climate Calculator, by World Resources Institute, which is short and asks only the hard numbers: therms, kWh, fuel economy and miles traveled, and rewards you at the end with a little animated guy who becomes a devil or angel depending on your emissions.

• TerraPass, like most if not all carbon offset providers, has a suite of calculators, including personal and business calculators as well as specific calculators for driving, flying, etc. Also typical, the only option to "take action" is to buy carbon offsets or other "green products. " None of these are designed to encourage behavioral change. Still, I liked that it allows users to input specific flights taken, rather than number of "short" or "long" flights, or total miles or hours traveled. This doesn't mean TerraPass's calculator is more accurate, while that is possible — all I know is it shows the lowest emissions on the Consumer Reports review, and I'd lean towards using one in the middle of the range in the absence of better info on accuracy.
• EPA provides a whole suite of calculators themselves (including ones for waste, recycled content and durable goods), and links to other's calculators — but what is especially useful for folks trying to get the word out is their GHG Equivalencies Calculator — which lets you input a consumption unit and get out how that number compares to barrels of oil consumed, tree seedlings grown, passenger vehicles, etc, etc. With this you can put emissions into terms anyone can understand.

What's next? Well, it looks like we'll be getting calculators like the "Carbon Hero" that calculates a user's carbon footprint from transportation as you move around, carrying the tiny data-collector with you. While I'm not sure whether this is really any better a calculator, I'm pretty sure it'll appeal to the gadget-geeks (but, we also need a hand-held one that calculates the embodied and operational carbon of each gadget they purchase). Unfortunately, the most noticeable thing about carbon calculators is still the plethora of options and the lack of consistency amongst them and we will applaud all efforts to clarify the field. In the mean time we still think trying out some of these calculators is a worthwhile effort to get people thinking, but we suggest taking the results and recommendations with more than a grain of salt.