What is the true cost of inflation?

I ask because last year fuel was around R13 a liter, this year it's already over R17.

Last year I bought my douglasdale milk from PNP at R23 for the 2 liters bottle. It's now R28

Last year we could easily get 2 liter Cokes on special for R13.99. This year we hardly get it on special.

So, if I had R100 000 last year, the buying power surely dropped more than 7%? And that R100 000 really has last value than R93 000 this year? So how much exactly is inflation? Or rather, how much increase in salary a person should get every year to have the same buying power?