The Kardashev scale is a metric used to grade how advanced some civilization is, in terms of total energy utilization. The usual grading goes from Type I (all the energy of a planet) to Type II (all the energy of a star) to Type III (all the energy of a galaxy) and there are some extrapolations beyond that. Carl Sagan used the values given by Kardashev to interpolate non-integer scores for civilizations, with the following equation
where is the Kardashev score and is the average power output. A Type I civilization would have , Type II would have , and so on. So now we need some numbers.
According to a BP overview of worldwide energy consumption (page 40, “Total World”), in 2012 the energy consumption amounted to 12,476.6 million tonnes of oil equivalent, where a “megatoe” is joules. Therefore, we get
Which when we put into the first equation we get
The Wikipedia page uses 2008 numbers and gets 0.717, so we’ve gone up a few points in the past few years, if these numbers are right. I’d be fairly confident of 0.7, somewhat confident about 0.72, and less-so about 0.725.
EDIT: Using data from the EIA’s database for world total primary energy consumption, I found historical values of: