How to calculate %increase
 

Ok I know this is a stupid question but I just have been doing some cals and I'm averaging 9.789274L/100km in the city in a Chevey Optra (Suzuki Reno) that is rated at 12.4L/100km in the city so any help figuring out my % increase would be appreciated.

You want the percent difference formula:

((new - old) / old) x 100 = Percent difference.

Example: A driver improved from 15 to 18mpg

((18-15)/15) = .2
.2 x 100 = 20
20% improvement

Not a stupid question at all.

Take your 12.4 and divide that by 9.789 to arrive at 1.2667, or 26.67% better.

Thanks for the calculation this should help out greatly