A basic carbon calculator offers a ballpark figure of a person's, business's or household's "carbon footprint" — that is, all the greenhouse gases emitted either directly or on one's behalf. A good carbon calculator will offer tips for minimizing your carbon footprint and many will allow you to calculate how to offset it. There are limits to what a carbon calculator can provide, though; you should consider your calculation an estimate only. It helps if you have accurate information before you start, such as a precise idea of how much energy you use at home or how many miles you drive in a day.
Online carbon calculators for individuals or households
Conservation International: Short calculator that factors in living conditions, automobile information and air travel. Not in-depth but offers a nice, quick estimate of your carbon footprint and suggests how much money it takes to offset your footprint.
The Nature Conservancy: This calculator is not too long and not too short. It calculates for individuals or households by state and offers great tips at the end plus handy pie charts.
EPA Household Emissions Calculator: An excellent, in-depth calculator that takes about 15-20 minutes to complete. Issues covered include home energy use, household vehicle use, recycling and more. There are handy recommendations and questions at the end such as, "You could turn down your thermostat by 5 degrees — will you do this?" If you commit to a step the EPA recommends it shows you how much you'll save in money and CO2 emissions.
Carbon Domestic Household Calculator: This calculator is offered for most areas of the world and offers some rare carbon calculations such as motorbike and train transport.
Online carbon calculators for businesses
The Greenhouse Gas Protocol: This site offers business-oriented tools for calculating carbon, such as emissions from employee commuting or from working with various materials such as metals or lime. The downside is that the tools aren't automatically calculated. Tools are offered in electronic Excel spreadsheet form with step-by-step guidance documents. If you need a highly specific calculation, however, such as, "CO2 emissions from the production of cement," then this is a great site.
Carbon Trust toolkit: U.K.-based carbon calculators that help measure and manage you environmental impact.
Target Finder: This quick Energy Star calculator allows architects or folks in the construction industry to plan an energy-efficient target for building projects, which, of course, lowers that building's emissions.
Online carbon calculators for little tree huggers
Zerofootprint Kids Calculator: Well-done carbon calculator for kids. Covers information related to food, travel, recycling and more in a bright, interactive way. Carbon terms are explained in a manner kids can understand.