Ever wondered how big your own carbon footprint might be?

...and Juliette says

It was mostly easy to use, but difficult to correct mistakes. There's a charming section with recommendations for reducing your footprint. For example: water your plants in the early morning or late evening and 'watch the Live Lightly tree grow' as you do your bit. Again, there are no figures appended to help you prioritise.

Rating: 5/10

3. WWF

footprint.wwf.org.uk

· Takes 6 minutes

The calculator says...

You bad, bad person. Or, more specifically, 13.4 tonnes. That's more than double the Defra calculation, and much higher than the others reviewed here too. 'It's not all down to you,' it adds, more mollifyingly. Much of this, it suggests, is because many goods and services we use are not produced as efficiently as they could be - something 'UK government and business' need to sort out, claims WWF.

...and Juliette says

As well as the usual home and travel sections, this includes a more detailed food section than others, and, almost uniquely, a 'stuff' section, which asks about how much we consume, from buying jewellery and replacing electrical goods to keeping pets and doing DIY. There are varied and engaging recommendations (buy more seasonal food, for example), albeit with no figures on consequent carbon savings, and interesting blogs on things like planning a green wedding. The best calculator, but NEF has the edge on recommendations.

Rating: 8/10

4. Best Foot Forward

www.bestfootforward.com/carbonlife.htm

· Takes 2-3 minutes

The calculator says...

My tally is 7.4 tonnes of CO2, which, it calculates, requires 4.3 hectares of the planet's surface to absorb. 'If everybody lived like you, we would need 2.6 planets to support global consumption,' it adds. In spite of that, I have a footprint smaller than the British average, according to this way of looking at things.

...and Juliette says

This is quick and simple, so much of the calculation assumes national averages, particularly your share of emissions to produce goods and services. Otherwise, it relies on generalisations (do you 'tend to conserve energy'?), but it does ask about areas ignored by most calculators: food and waste. There are no recommendations, but you can pay for more detailed services.

Rating: 4/10

5. NEF

www.nef.org.uk/actonCO2/carboncalculator.htm

· Takes 8 minutes

The calculator says...

NEF's calculator allows for 'radiative forcing' - multiplying greenhouse gases from flights two to four times to account for the fact that high-altitude emissions do more damage. Given that, the tally seems very low at 8.14 tonnes. Interestingly, it compares the total to what average per-capita emissions will have to fall to in future: 4.5 tonnes in 2020. That's a big cut.

...and Juliette says

The recommendations section is brilliant. A few suggestions related to things it didn't ask about and that I had in fact already done, raising doubts about the actual calculation. But for each pledge you make, it tells you how much carbon you would save: such as 'I will buy a solar water heater (-0.11 tonnes) and 'I will not fly any more' (lots).

Rating: 9/10

Top tips: Personal shopper

Before you start, it's worth having a few things to hand or you'll spend half the time scrabbling around trying to find out all sorts of things you hadn't realised you didn't know.

Most importantly have your gas and electricity bills to hand, preferably a year's worth. If that's not possible, ring your utility companies and ask. Have a (real) calculator to hand as well - every website seems to ask for a different version of this information. Your MOT certificate is also helpful to check your mileage over the previous year and (just in case) the car's engine size.

You'll also need to know about your home for most of the calculators: what insulation you have, and where; what kind of boiler you use; and the energy rating of your appliances.

Finally, before you start, have a think about all your flights in the past year, and any other regular or long-distance rail and bus trips you made.