MT's Cost Tables' author, John Phillips, has come up with this simple formula to calculate CO2 emissions from mpg figures.
- Take the mpg figure and convert to km/litre by multiplying by 0.352.
- Divide 1 by the km/litre figure to give the litre/km figure.
- Multiply this by 2.63 to give the CO2 produced in kg/km.
- Multiply this by 1,000 to convert it to g/km, the standard unit.
"It's not too difficult - it just has to be done methodically," says Phillips. "For example, if you have a 44-tonner returning 7.2mpg; 7.2 multiplied by 0.352 gives you 2.53km/litre; 1 divided by 2.53 gives you 0.395 litre/km; 0.395 multiplied by 2.63 gives you 1.04kg of CO2/km; finally that figure multiplied by 1,000 gives you 1,040g of CO2/km. To work out your total emissions, multiply that final figure by your mileage 
in km."