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.

The Carbon Neutral Company: Calculate your household or personal transportation footprint; the site divides us into two categories: "North America" or "Europe & the rest of the world."

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.

EarthLab: This calculator breaks down vehicle information by car type, which not all calculators do. Plus you get your own carbon Web page at the end where you can make green pledges and learn how to lower your footprint.

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 Carbon Neutral Company: Excellent U.K.-based business carbon calculator that's more in-depth than many others. This company also offers an easy getting started guide.

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: U.K.-based carbon calculator that breaks downemissions by specific job sectors.

Carbon Footprint Business Calculator: For businesses in North America and many other areas of the world. The sign-up process requires you to give your workplace information, so be prepared.

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.

The Campus Carbon Calculator: This calculator is perfect for school staff or students and estimates college campus emissions in both the United States and Canada.

Online carbon calculators for little tree huggers

Carbon Slayer: A fun "carbon piggy" calculator for Australian youth.

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.

Bobbie Bigfoot Calculator: Uses visuals in the questions, which makes this a good calculator for younger kids to do with a parent.